Look for tags along the master branch checkout out Zstd

Summary:
There is no guarantee that the default branch in git is 'master'; so
    unless specified we checkout a tag along the 'dev' branch, which is not
    intended as it is the master branch that tracks releases for Zstd.

Reviewed By: jstrizich

Differential Revision: D8297843

fbshipit-source-id: 8497dc75c399ae7c86e27b28fdb73898ef4b1a4e

build/fbcode_builder/specs/zstd.py

@@ -11,7 +11,7 @@ def fbcode_builder_spec(builder):
     # This API should change rarely, so build the latest tag instead of master.
     builder.add_option(
         'facebook/zstd:git_hash',
-        ShellQuoted('$(git describe --abbrev=0 --tags)')
+        ShellQuoted('$(git describe --abbrev=0 --tags origin/master)')
     )
     return {
         'steps': [