Fix link to container image in linux instructions (#82409)

I suppose head of the URL was redondant — gave me "docker: invalid refence format" when I tried the original command, and worked fine when I removed the first "mcr.microsoft.com/dotnet-buildtools/prereqs:"

diff --git a/docs/workflow/building/coreclr/linux-instructions.md b/docs/workflow/building/coreclr/linux-instructions.md
index dab3981..de38b55 100644 (file)
--- a/docs/workflow/building/coreclr/linux-instructions.md
+++ b/docs/workflow/building/coreclr/linux-instructions.md
@@ -30,7 +30,7 @@ Please note that choosing the same image as the host OS you are running on will
 Once you have chosen an image, the build is one command run from the root of the runtime repository:
 
 ```bash
-docker run --rm -v <RUNTIME_REPO_PATH>:/runtime -w /runtime mcr.microsoft.com/dotnet-buildtools/prereqs:mcr.microsoft.com/dotnet-buildtools/prereqs:centos-7-20210714125435-9b5bbc2 ./build.sh --subset clr
+docker run --rm -v <RUNTIME_REPO_PATH>:/runtime -w /runtime mcr.microsoft.com/dotnet-buildtools/prereqs:centos-7-20210714125435-9b5bbc2 ./build.sh --subset clr
 ```
 
 Dissecting the command: