Optimize _.invert, _.pairs, and _.values.

Former-commit-id: d2725dc8c75254784d450f2a7e997e079b8c3183

build.js

@@ -97,7 +97,7 @@
     'indexOf': ['sortedIndex'],
     'initial': [],
     'intersection': ['indexOf'],
-    'invert': ['forOwn'],
+    'invert': ['keys'],
     'invoke': ['forEach'],
     'isArguments': [],
     'isArray': [],
@@ -129,7 +129,7 @@
     'object': [],
     'omit': ['forIn', 'indexOf'],
     'once': [],
-    'pairs': ['forOwn'],
+    'pairs': ['keys'],
     'partial': ['isFunction', 'isObject'],
     'pick': ['forIn'],
     'pluck': ['map'],
@@ -155,7 +155,7 @@
     'uniq': ['identity', 'indexOf'],
     'uniqueId': [],
     'value': ['mixin'],
-    'values': ['forOwn'],
+    'values': ['keys'],
     'where': ['filter', 'keys'],
     'without': ['indexOf'],
     'wrap': [],