Stop telling people to run npm rebuild with --force

This forces a local compilation (slow) when they just want to
download right binary (fast).

lib/errors.js

@@ -25,7 +25,7 @@ function foundBinariesList() {
 function missingBinaryFooter() {
   return [
     'This usually happens because your environment has changed since running `npm install`.',
-    'Run `npm rebuild node-sass --force` to build the binding for your current environment.',
+    'Run `npm rebuild node-sass` to download the binding for your current environment.',
   ].join('\n');
 }