feat: way to avoid github API limit (#122)

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<!-- What changes are being made? (What feature/bug is being fixed here?) -->
**What**:
Add a way to avoid GITHUB API LIMIT by supplying an optional GITHUB_AUTH token to increase github rate limiting from 50 requests to 5000 (and limited by user, not IP)

<!-- Why are these changes necessary? -->
**Why**:
To address: #121 

<!-- How were these changes implemented? -->
**How**:
By Me

<!-- Have you done all of these things?  -->
**Checklist**:
<!-- add "N/A" to the end of each line that's irrelevant to your changes -->
<!-- to check an item, place an "x" in the box like so: "- [x] Documentation" -->
- [ ] Documentation
- [ ] Tests
- [ ] Ready to be merged <!-- In your opinion, is this ready to be merged as soon as it's reviewed? -->
- [ ] Added myself to contributors table <!-- this is optional, see the contributing guidelines for instructions -->

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src/repo/github.js

@@ -1,6 +1,19 @@
 const pify = require('pify')
 const request = pify(require('request'))
 
+function getRequestHeaders() {
+  const requestHeaders = {
+    'User-Agent': 'request',
+  }
+
+  const optionalAuthToken = process.env.GITHUB_TOKEN
+  if (optionalAuthToken) {
+    requestHeaders.Authorization = `token ${optionalAuthToken}`
+  }
+
+  return requestHeaders
+}
+
 function getNextLink(link) {
   if (!link) {
     return null
@@ -19,9 +32,7 @@ function getContributorsPage(url) {
   return request
     .get({
       url,
-      headers: {
-        'User-Agent': 'request',
-      },
+      headers: getRequestHeaders(),
     })
     .then(res => {
       const body = JSON.parse(res.body)
@@ -54,9 +65,7 @@ const getUserInfo = function(username, hostname) {
   return request
     .get({
       url: `${root}/users/${username}`,
-      headers: {
-        'User-Agent': 'request',
-      },
+      headers: getRequestHeaders(),
     })
     .then(res => {
       const body = JSON.parse(res.body)