fix(install): don't use option '-e' for builtin echo

echo is often a builtin and '-e' is not an option for sh.
sh is the default shell for gnu make (variable "SHELL") -> this leads to an
extra "-e" in .gitignore

install.sh

@@ -20,9 +20,9 @@ main() {
     if [ ! -f .gitignore ]; then
         touch .gitignore
     fi
-    grep -qFx -- "$TASKS_DIR/" .gitignore || echo -e "$TASKS_DIR/" >> .gitignore
+    grep -qFx -- "$TASKS_DIR/" .gitignore || echo "$TASKS_DIR/" >> .gitignore
 
     echo "Done"
 }
 
-main
+main