Fixed mainTemplate.gradle patching regression.

Fixed Android Resolver mainTemplate.gradle patcher regression on
Windows introduced by I3208790dcd8a515982654ccb56ad0ccbcf1ed4f8.
Maven paths are file URIs which require POSIX directory separators
rather than the Windows native directory separators.

For example...

Invalid - 'file:///Assets/GeneratedLocalRepo\Firebase/m2repository'
Valid   - 'file:///Assets/GeneratedLocalRepo/Firebase/m2repository'

Fixes #361

Change-Id: I2ece2cbd6bff3a3eade6360e9234b6ecaec19376

Author: Stewart Miles

source/AndroidResolver/src/PlayServicesResolver.cs

@@ -1958,8 +1958,9 @@ internal static IList<string> GradleMavenReposLines(ICollection<Dependency> depe
                     string repoUri;
                     if (repoAndSources.Key.StartsWith(projectFileUri) && !exportEnabled) {
                         var repoPath = repoAndSources.Key.Substring(projectFileUri.Length + 1);
-                        repoPath = FileUtils.ReplaceBaseAssetsOrPackagesFolder(
-                                repoPath, GooglePlayServices.SettingsDialog.LocalMavenRepoDir);
+                        repoPath = FileUtils.PosixPathSeparators(
+                            FileUtils.ReplaceBaseAssetsOrPackagesFolder(
+                                repoPath, GooglePlayServices.SettingsDialog.LocalMavenRepoDir));
                         repoUri = String.Format("(unityProjectPath + \"/{0}\")", repoPath);
                     } else {
                         repoUri = String.Format("\"{0}\"", repoAndSources.Key);