[CS2] Require Node 6.9.1+ (#4341)

* Node 6 deprecated `new Buffer` in favor of `Buffer.from` and `Buffer.alloc`; update our calls, and set the required version of Node to be >= 6.9.0, and set this to be 2.0.0-alpha for now

* Bump to Node version 6.9.1

test/repl.coffee

@@ -13,7 +13,7 @@ class MockInputStream extends Stream
   resume: ->
 
   emitLine: (val) ->
-    @emit 'data', new Buffer("#{val}\n")
+    @emit 'data', Buffer.from("#{val}\n")
 
 class MockOutputStream extends Stream
   constructor: ->
@@ -21,7 +21,7 @@ class MockOutputStream extends Stream
     @written = []
 
   write: (data) ->
-    #console.log 'output write', arguments
+    # console.log 'output write', arguments
     @written.push data
 
   lastWrite: (fromEnd = -1) ->