Use newer formidable - fixes Node 6.x compat

Hi - there's a newer (but not very new) update to Formidable which contains a fix to support Node 6.x:

node-formidable/formidable@f4a3e08
node-formidable/formidable#364
node-formidable/formidable#404

Author: mikeatlas

package.js

@@ -25,7 +25,7 @@ Package.onUse(function(api) {
 //});
 
 Npm.depends({
-  formidable: '1.0.15',
+  formidable: '1.0.17',
   imagemagick: '0.1.3',
   connect: '2.7.10'
 })