Missing user.githubuser causes 'Uncaught, unspecified "error" event'

[rexwhite]

First of all: nice work!

Second, if the user hasn't previously saved their github user id then your generator throws 'Uncaught, unspecified "error" event.' This happens because getUsername() in src/generators/shared/shell.es6 rejects its promise if "git config --get user.githubuser" returns non-zero, which it will if user.githubuser has never been saved.

I suggest just returning "resolve('')" instead.

diff --git a/generators/shared/shell.js b/generators/shared/shell.js
index 2eb601d..25aca7c 100644
--- a/generators/shared/shell.js
+++ b/generators/shared/shell.js
@@ -26,7 +26,7 @@ function getUsername() {
 
     _shelljs2.default.exec('git config --get user.githubuser', { silent: true }, (code, stdout, stderr) => {
       if (code !== 0) {
-        return reject(stderr);
+        return resolve('');
       }
       return resolve(stdout.trim());
     });