stream should not pass extension

Author: mattdesl

lib/save.js

@@ -23,6 +23,7 @@ function stream (isStart, opts = {}) {
   return new Promise((resolve, reject) => {
     opts = assign({}, defaultExts, opts);
     const filename = resolveFilename(Object.assign({}, opts, {
+      extension: '',
       frame: undefined
     }));
     const func = isStart ? 'streamStart' : 'streamEnd';