Updates the request transport to pass through file objects to the Sla…

…ck API correctly, by switching to formData mode with the request module when a file is supplied in the args to an API method.

Fixes #103

lib/clients/transports/request.js

@@ -3,6 +3,7 @@
  */
 
 var HttpsProxyAgent = require('https-proxy-agent');
+var has = require('lodash').has;
 var partial = require('lodash').partial;
 var request = require('request');
 
@@ -22,11 +23,18 @@ var handleRequestTranportRes = function handleRequestTranportRes(cb, err, respon
 
 
 var getRequestTransportArgs = function getReqestTransportArgs(args) {
-  return {
+  var transportArgs = {
     url: args.url,
-    form: args.data,
     headers: args.headers,
   };
+
+  if (has(args.data, 'file')) {
+    transportArgs.formData = args.data;
+  } else {
+    transportArgs.form = args.data;
+  }
+
+  return transportArgs;
 };