Respect the LIBSASS_EXT build flag when falling back to git

Author: xzyfer

scripts/build.js

@@ -101,7 +101,9 @@ function initSubmodules(cb) {
 function installGitDependencies(cb) {
   var libsassPath = './src/libsass';
 
-  if (fs.access) { // node 0.12+, iojs 1.0.0+
+  if (process.env.LIBSASS_EXT) {
+    cb();
+  } else if (fs.access) { // node 0.12+, iojs 1.0.0+
     fs.access(libsassPath, fs.R_OK, function(err) {
       err && err.code === 'ENOENT' ? initSubmodules(cb) : cb();
     });