Const and comparison fixes.

h/t @YuriSolovyov

src/git-repository-async.js

@@ -346,14 +346,9 @@ module.exports = class GitRepositoryAsync {
     return this.repoPromise
       .then(repo => repo.openIndex())
       .then(index => {
-        let entry = index.getByPath(_path)
-        let submoduleMode = 57344 // TODO compose this from libgit2 constants
-
-        if (entry.mode === submoduleMode) {
-          return true
-        } else {
-          return false
-        }
+        const entry = index.getByPath(_path)
+        const submoduleMode = 57344 // TODO compose this from libgit2 constants
+        return entry.mode === submoduleMode
       })
   }
 }