Add try/catch in very rare scenario of html being returned instead of…

… json. this 90% appears to be because of a timeout blip recently

lib/sendgrid.js

@@ -79,8 +79,15 @@ var Sendgrid = function(api_user, api_key, options) {
       method    : 'POST',
       uri       : "https://sendgrid.com/api/mail.send.json"
     }, function(err, resp, body) {
+      var json;
+
       if(err) return callback(err, null);
-      var json = JSON.parse(body);
+
+      try {
+        json = JSON.parse(body);
+      } catch (e) {
+        return callback(new Error(e), null);
+      }
 
       if (json.message !== 'success') {
         var error = 'sendgrid error';