Use API URL when connecting to GitHub:Enterprise

When using a hosted GitHub (e.g. GitHub:Enterprise) we need to 
make sure the URL is used not only for the OAuth handshake
but also for the GitHub API endpoint.

Change-Id: I7904b8cb0a00f6e375826f3a0674c6a341c0e112

github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java

diff --git a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java
index 081d6c1..f9afeeb 100644
--- a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java
+++ b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java
@@ -136,7 +136,7 @@
   }
 
   public GitHub getHub() throws IOException {
-    return GitHub.connectUsingOAuth(this.token.accessToken);
+    return GitHub.connectUsingOAuth(config.gitHubApiUrl, token.accessToken);
   }
 
   private String getScopesKey(HttpServletRequest request,