Fix #8: only invoke callback if it's a function

Author: Anthony Nowell

lib/algorithm.js

@@ -28,7 +28,7 @@ Algorithm = (function() {
       'Content-Type': contentType
     }, (function(_this) {
       return function(response, status) {
-        return _this.callback(new AlgoResponse(response, status));
+        return typeof _this.callback === "function" ? _this.callback(new AlgoResponse(response, status)) : void 0;
       };
     })(this));
     return this.promise;

src/algorithm.coffee

@@ -25,7 +25,7 @@ class Algorithm
       'POST',
       data,
       {'Content-Type': contentType},
-      (response, status) => @callback(new AlgoResponse(response, status))
+      (response, status) => @callback?(new AlgoResponse(response, status))
     )
 
     @promise