chore(package): update danger to version 2.0.0-alpha.20

Author: greenkeeper[bot]

package.json

@@ -103,7 +103,7 @@
     "babel-jest": "21.2.0",
     "babel-plugin-flow-react-proptypes": "6.1.0",
     "babel-preset-react-native": "3.0.1",
-    "danger": "2.0.0-alpha.19",
+    "danger": "2.0.0-alpha.20",
     "eslint": "4.9.0",
     "eslint-config-prettier": "2.6.0",
     "eslint-plugin-babel": "4.1.2",