lint - warn on unhandled err

.eslintrc

@@ -44,7 +44,7 @@
     "eol-last": 1,
     "eqeqeq": [2, "allow-null"],
     "generator-star-spacing": [2, { "before": true, "after": true }],
-    "handle-callback-err": [2, "^(err|error)$" ],
+    "handle-callback-err": [1, "^(err|error)$" ],
     "indent": [2, 2, { "SwitchCase": 1 }],
     "jsx-quotes": [2, "prefer-single"],
     "key-spacing": [2, { "beforeColon": false, "afterColon": true }],
@@ -145,6 +145,6 @@
     "wrap-iife": [2, "any"],
     "yield-star-spacing": [2, "both"],
     "yoda": [2, "never"],
-    "prefer-const": 1
+    "prefer-const": 1,
   }
 }