Switch variable use to be less repetitive.

Some of these were already defined higher up, so it's worth using their
shorter notations!

dangerfile.ts

@@ -3,8 +3,9 @@ import { includes } from 'lodash';
 import * as fs from 'fs';
 
 // Setup
-const pr = danger.github.pr;
-const commits = danger.github.commits;
+const github = danger.github;
+const pr = github.pr;
+const commits = github.commits;
 const modified = danger.git.modified_files;
 const bodyAndTitle = (pr.body + pr.title).toLowerCase();
 console.log(commits.map(({ sha }) => sha));
@@ -24,8 +25,8 @@ const modifiedAppFiles = modified
 
 // Takes a list of file paths, and converts it into clickable links
 const linkableFiles = paths => {
-  const repoURL = danger.github.pr.head.repo.html_url;
-  const ref = danger.github.pr.head.ref;
+  const repoURL = pr.head.repo.html_url;
+  const ref = pr.head.ref;
   const links = paths.map(path => {
     return createLink(`${repoURL}/blob/${ref}/${path}`, path);
   });
@@ -92,7 +93,7 @@ if (!isBot) {
   // Warn when there is a big PR
   const bigPRThreshold = 500;
   if (
-    danger.github.pr.additions + danger.github.pr.deletions >
+    github.pr.additions + github.pr.deletions >
     bigPRThreshold
   ) {
     warn(':exclamation: Big PR');