feat: add persistent file logger to record the errors occured in webh…

…ooks.

index.js

@@ -1,6 +1,7 @@
 const Issue = require('./src/issue');
 const text = require('./src/text');
 const { isCommitter } = require('./src/coreCommitters');
+const logger = require('./src/logger');
 
 module.exports = ({ app }) => {
     app.on(['issues.opened'], async context => {
@@ -165,6 +166,11 @@ module.exports = ({ app }) => {
             return Promise.all([addLabel, removeLabel]);
         }
     });
+
+    app.webhooks.onError(error => {
+        logger.error('bot occured an error');
+        logger.error(error);
+    });
 }
 
 function getRemoveLabel(context, name) {