added caching of node modules

.travis.yml

@@ -31,6 +31,10 @@ env:
   - arch=x64
   - configuration=Release  
   - os_platform=linux
+
+cache:
+  directories:
+  - node_modules
   
 # Work around NuGet issue #2163
 # https://github.com/NuGet/Home/issues/2163

appveyor.yml

@@ -41,6 +41,10 @@ environment:
     arch: ia32
     plat: win32
 
+# build cache to preserve files/folders between builds
+cache:
+  - node_modules
+  
 init:
 - ps: |
       $env:log_prefix = "[$env:win_runtime][$env:configuration]"