Upgrade: debug@^3.1.0

This version of debug addresses a minor ReDoS issue. See debug-js/debug#501, debug-js/debug#504 for more information. Looking at the rest of the changelog, this should be a pretty low-risk upgrade.

package.json

@@ -39,7 +39,7 @@
     "chalk": "^2.1.0",
     "concat-stream": "^1.6.0",
     "cross-spawn": "^5.1.0",
-    "debug": "^3.0.1",
+    "debug": "^3.1.0",
     "doctrine": "^2.0.2",
     "eslint-scope": "^3.7.1",
     "espree": "^3.5.2",