Merge pull request #267: Update Git to include concurrent pack-file fix

These updates allow the gvfs-helper to be more resilient to concurrent pack downloads.

See microsoft/git#229 and microsoft/git#231 for more details.

Author: derrickstolee

Directory.Build.props

@@ -36,7 +36,7 @@
 
     <!-- Version information -->
     <ScalarVersion>0.2.173.2</ScalarVersion>
-    <GitPackageVersion>2.20191217.3</GitPackageVersion>
+    <GitPackageVersion>2.20191231.1</GitPackageVersion>
     <WatchmanPackageUrl>https://github.com/facebook/watchman/suites/307436006/artifacts/304557</WatchmanPackageUrl>
     <GcmCoreOSXPackageUrl>https://github.com/microsoft/Git-Credential-Manager-Core/releases/download/v2.0.79-beta/gcmcore-osx-2.0.79.64449.pkg</GcmCoreOSXPackageUrl>
 

Scalar.Installer.Mac/InstallScalar.template.sh

@@ -106,6 +106,7 @@ if [ $INSTALL_WATCHMAN -eq 1 ]; then
     echo "Installing watchman as: $CURRENT_USER"
 
     sudo -u $CURRENT_USER brew update
+    sudo -u $CURRENT_USER brew unlink python@2 || echo "Python 2 was not installed"
     sudo -u $CURRENT_USER brew install watchman
 else
     echo ""