Gracefully handle partial git info.

On some host/git combinations, gitRepoInfo returns an object like the
following:

`{ sha: null, abbreviatedSha: null, branch: 'develop', tag: null }`

When using the version-commit option, ember-cli-deploy would fail if the sha
is empty.

Author: cball

README.md

@@ -156,6 +156,8 @@ The unique identifier of this build based on the version in the `package.json`,
 
 For example, if your package.json version is `v2.0.3`, and the current commit is `0993043d49f9e0[...]`, this generator will return a revision of `v2.0.3+0993043d`.
 
+`Note:` Some environments (like CircleCI) may return partial git information. If the current commit hash cannot be determined, the generator will return only the package.json version (`v2.0.3`) as the `revisionKey`.
+
 ##### timestamp
 
 The timestamp of the current deploy

lib/data-generators/version-commit.js

@@ -21,18 +21,26 @@ module.exports = CoreObject.extend({
     }
 
     var info = gitRepoInfo(path);
-    var sha = info.sha.slice(0, 8);
+    var sha = (info.sha || '').slice(0, 8);
+    var log = this._plugin.log;
 
     return readFile(versionFile)
       .then(function(contents) {
         var json = JSON.parse(contents);
 
-        if (!json.version || !sha) {
+        if (!json.version) {
           return Promise.reject('Could not build revision with version `' + json.version + '` and commit hash `' + sha + '`');
         }
 
+        var versionString = json.version;
+        if (sha) {
+          versionString = versionString + '+' + sha;
+        } else {
+          log('Missing git commit sha, using package version as revisionKey', { color: 'yellow', verbose: true });
+        }
+
         return {
-          revisionKey: json.version + '+' + sha,
+          revisionKey: versionString,
           timestamp: new Date().toISOString()
         };
       });

tests/fixtures/repo/dotgit-branch-only/HEAD

@@ -0,0 +1 @@
+ref: refs/heads/master

tests/fixtures/repo/dotgit-branch-only/config

@@ -0,0 +1,7 @@
+[core]
+	repositoryformatversion = 0
+	filemode = true
+	bare = false
+	logallrefupdates = true
+	ignorecase = true
+	precomposeunicode = true

tests/fixtures/repo/dotgit-branch-only/index

@@ -0,0 +1,2 @@
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