Install Sass in the Docker base image

* Install node-sass in Dockerfile-base
* Update Makefile "echo" for "compilecss" step
* Update node-sass call to use "--source-map true"
  (see sass/node-sass#1026)

Dockerfile-base

@@ -37,7 +37,7 @@ RUN npm install -g \
     cssmin@0.4.3 \
     csslint@0.10.0 \
     jshint@2.7.0 \
-    stylus@0.49.2 \
+    node-sass@4.3.0 \
     uglify-js@2.4.13 \
     clean-css@3.4.23
 ENV PIPELINE_CSS_COMPRESSOR=pipeline.compressors.cssmin.CSSMinCompressor \

Makefile

@@ -34,7 +34,7 @@ locust:
 	locust -f tests/performance/smoke.py --host=https://developer.allizom.org
 
 compilecss:
-	@ echo "## Compiling Stylus files to CSS ##"
+	@ echo "## Compiling Sass files to CSS ##"
 	@ ./scripts/compile-stylesheets
 
 compilejsi18n:

scripts/compile-stylesheets

@@ -26,16 +26,16 @@ STYLESHEETS=($SASSDIR/*.scss)
 if [ $WATCH ]; then
   echo Watching and automatically compiling stylesheets
 
-  # Using $STYLESHEETS directly so that sass only watches each stylesheet
+  # Using $STYLESHEETS directly so that node-sass only watches each stylesheet
   # once, even if it is @included multiple times.
   if [ $QUIET ]; then
-    (node-sass ${STYLESHEETS[@]} --output $CSSDIR --precision 3 --source-map --watch &) &> /dev/null
+    (node-sass ${STYLESHEETS[@]} --output $CSSDIR --precision 3 --source-map true --watch &) &> /dev/null
   else
-    node-sass ${STYLESHEETS[@]} --output $CSSDIR --precision 3 --source-map --watch
+    node-sass ${STYLESHEETS[@]} --output $CSSDIR --precision 3 --source-map true --watch
   fi
 else
   # Iterating through stylesheets so that shell output is immediate.
   for ss in ${STYLESHEETS[@]}; do
-    node-sass $ss --output $CSSDIR --precision 3 --source-map
+    node-sass $ss --output $CSSDIR --precision 3 --source-map true
   done
 fi