Fix incorrect eslint import errors

Just adds the development package `eslint-import-resolver-webpack`,
which is [already configured][0], but not previously installed. This
removes a _lot_ of incorrect eslint errors.

[0]: 2d344ef4ca/.eslintrc (L6-L10)

package.json

@@ -63,6 +63,7 @@
     "enzyme": "^2.4.1",
     "eslint": "^3.7.1",
     "eslint-config-netlify": "github:netlify/eslint-config-netlify",
+    "eslint-import-resolver-webpack": "^0.8.3",
     "exports-loader": "^0.6.3",
     "extract-text-webpack-plugin": "^2.1.2",
     "file-loader": "^0.11.2",