fix(grunt): cache version number

caching the version number speeds up the build and preserves resources.

this also fixed EMFILE error that now occurs on some macs.

lib/grunt/utils.js

@@ -2,6 +2,7 @@ var fs = require('fs');
 var shell = require('shelljs');
 var grunt = require('grunt');
 var spawn = require('child_process').spawn;
+var version;
 
 module.exports = {
 
@@ -11,6 +12,8 @@ module.exports = {
 
 
   getVersion: function(){
+    if (version) return version;
+
     var package = JSON.parse(fs.readFileSync('package.json', 'UTF-8'));
     var match = package.version.match(/^([^\-]*)(-snapshot)?$/);
     var semver = match[1].split('.');
@@ -18,7 +21,7 @@ module.exports = {
 
     var fullVersion = (match[1] + (match[2] ? '-' + hash : ''));
     var numVersion = semver[0] + '.' + semver[1] + '.' + semver[2];
-    var version = {
+    version = {
       number: numVersion,
       full: fullVersion,
       major: semver[0],