Install node-sass without keeping C++ and others librairies

something like 
```
+ RUN apk add --no-cache git
+ RUN apk add --no-cache --virtual .build-deps \
+        g++ \
+        make \
+        python \
+    && npm --quiet install --global node-sass \
+    && apk del .build-deps \
+    && rm -rf /tmp/*
```