Allow some fixtures to pass linting when XO is installed without lockfile

Author: novemberborn

test/fixture/long-stack-trace/package.json

@@ -1,5 +1,8 @@
 {
 	"ava": {
 		"require": "./enable-trace.js"
+	},
+	"dependencies": {
+		"bluebird": "*"
 	}
 }

test/fixture/trigger-worker-exception/package.json

@@ -1,5 +1,8 @@
 {
   "ava": {
     "require": "./hack.js"
-  }
+  },
+	"dependencies": {
+		"stack-utils": "*"
+	}
 }