Fixed filename case errors

Jakefile.js

@@ -83,8 +83,8 @@ task('build', {async: true}, function () {
       './src/graph/Groups.js',
       './src/graph/Images.js',
       './src/graph/graphMixins/physics/PhysicsMixin.js',
-      './src/graph/graphMixins/physics/BarnesHut.js',
-      './src/graph/graphMixins/physics/Repulsion.js',
+      './src/graph/graphMixins/physics/barnesHut.js',
+      './src/graph/graphMixins/physics/repulsion.js',
       './src/graph/graphMixins/ManipulationMixin.js',
       './src/graph/graphMixins/SectorsMixin.js',
       './src/graph/graphMixins/ClusterMixin.js',