Add nodejs-legacy to provide the 'node' command (#1004)

Affecting Ubuntu 16.04.3 LTS:

Following the directions of http://lemur.readthedocs.io/en/latest/quickstart/index.html, the make release command fails as the command 'node' cannot be found.

Adding nodejs-legacy solves the issue and allows the build to complete.

(lemur) lemur@lemur1:/www/lemur$ make release
--> Installing dependencies
npm install
npm WARN deprecated gulp-minify-css@1.2.4: Please use gulp-clean-css
npm WARN deprecated bower@1.8.2: ...psst! Your project can stop working at any moment because its dependencies can change. Prevent this by migrating to Yarn                                                                                 : https://bower.io/blog/2017/how-to-migrate-away-from-bower/
npm WARN deprecated gulp-foreach@0.1.0: Either use gulp-tap or gulp-flatmap, depending on your needs
npm WARN deprecated express@2.5.11: express 2.x series is deprecated
npm WARN deprecated connect@1.9.2: connect 1.x series is deprecated
npm WARN deprecated minimatch@2.0.10: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated minimatch@0.2.14: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated graceful-fs@1.2.3: graceful-fs v3.0.0 and before will fail on node releases >= v7.0. Please update to graceful-fs@^4.0.0 as soon as poss                                                                                 ible. Use 'npm ls graceful-fs' to find it in the tree.
npm WARN deprecated node-uuid@1.4.8: Use uuid module instead
npm WARN deprecated minimatch@0.3.0: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN prefer global marked@0.3.6 should be installed with -g

> optipng-bin@3.1.4 postinstall /www/lemur/node_modules/optipng-bin
> node lib/install.js

sh: 1: node: not found
npm WARN install:optipng-bin@3.1.4 optipng-bin@3.1.4 postinstall: `node lib/install.js`
npm WARN install:optipng-bin@3.1.4 spawn ENOENT

> jpegtran-bin@3.2.0 postinstall /www/lemur/node_modules/jpegtran-bin
> node lib/install.js

sh: 1: node: not found
npm WARN install:jpegtran-bin@3.2.0 jpegtran-bin@3.2.0 postinstall: `node lib/install.js`
npm WARN install:jpegtran-bin@3.2.0 spawn ENOENT

> gifsicle@3.0.4 postinstall /www/lemur/node_modules/gifsicle
> node lib/install.js

sh: 1: node: not found
npm WARN install:gifsicle@3.0.4 gifsicle@3.0.4 postinstall: `node lib/install.js`
npm WARN install:gifsicle@3.0.4 spawn ENOENT

> Lemur@ postinstall /www/lemur
> bower install --allow-root --config.interactive=false

/usr/bin/env: ‘node’: No such file or directory


Makefile:24: recipe for target 'release' failed
make: *** [release] Error 1
(lemur) lemur@lemur1:/www/lemur$ which node
(lemur) lemur@lemur1:/www/lemur$

Installing the package to solve the issue.

vsnine@lemur1:~$ sudo apt-get install nodejs-legacy
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  nodejs-legacy
0 upgraded, 1 newly installed, 0 to remove and 79 not upgraded.
Need to get 27.7 kB of archives.
After this operation, 81.9 kB of additional disk space will be used.
Get:1 http://ca.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 nodejs-legacy all 4.2.6~dfsg-1ubuntu4.1 [27.7 kB]
Fetched 27.7 kB in 0s (52.4 kB/s)
Selecting previously unselected package nodejs-legacy.
(Reading database ... 73230 files and directories currently installed.)
Preparing to unpack .../nodejs-legacy_4.2.6~dfsg-1ubuntu4.1_all.deb ...
Unpacking nodejs-legacy (4.2.6~dfsg-1ubuntu4.1) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up nodejs-legacy (4.2.6~dfsg-1ubuntu4.1) ...
vsnine@lemur1:~$ which node
/usr/bin/node
vsnine@lemur1:~$

docs/quickstart/index.rst

@@ -27,7 +27,7 @@ If installing Lemur on a bare Ubuntu OS you will need to grab the following pack
 .. code-block:: bash
 
     $ sudo apt-get update
-    $ sudo apt-get install nodejs python-pip python-dev python3-dev libpq-dev build-essential libssl-dev libffi-dev libsasl2-dev libldap2-dev nginx git supervisor npm postgresql
+    $ sudo apt-get install nodejs nodejs-legacy python-pip python-dev python3-dev libpq-dev build-essential libssl-dev libffi-dev libsasl2-dev libldap2-dev nginx git supervisor npm postgresql
 
 .. note:: PostgreSQL is only required if your database is going to be on the same host as the webserver.  npm is needed if you're installing Lemur from the source (e.g., from git).