Build before running karma tests

The test suite depends on the dist/ files. Running `npm test` after a
fresh git clone will fail unless `npm run build` is run first.

Author: dgraham

package.json

@@ -12,7 +12,7 @@
     "lint": "eslint include-fragment-element.js test/*.js",
     "prebuild": "npm run clean && npm run lint && mkdir dist",
     "build": "babel include-fragment-element.js -o dist/index-umd.js",
-    "pretest": "npm run lint",
+    "pretest": "npm run build",
     "test": "karma start ./test/karma.config.js",
     "prepublishOnly": "npm run build"
   },