bumping git version and adding hash validation

Author: pennywisdom

golang/Dockerfile

@@ -2,10 +2,12 @@ FROM golang:1.8-nanoserver
 
 SHELL ["powershell", "-Command", "$ErrorActionPreference = 'Stop'; $ProgressPreference = 'SilentlyContinue';"]
 
-ENV GIT_VERSION 2.11.0
+ENV GIT_VERSION 2.12.0
 ENV GIT_DOWNLOAD_URL https://github.com/git-for-windows/git/releases/download/v${GIT_VERSION}.windows.1/MinGit-${GIT_VERSION}-64-bit.zip
+ENV GIT_SHA256 6238f65c4d8412b993cb092efde4954f8cb7da4def54d0c1533835f00e83fdad
 
 RUN Invoke-WebRequest -UseBasicParsing $env:GIT_DOWNLOAD_URL -OutFile git.zip; \
+    if ((Get-FileHash git.zip -Algorithm sha256).Hash -ne $env:GIT_SHA256) {exit 1} ; \
     Expand-Archive git.zip -DestinationPath C:\git; \
     Remove-Item git.zip; \
     Write-Host 'Updating PATH ...'; \