git_repository: properly quote shallow argument
git_repository: properly quote shallow argument

Since fully qualified timestamps for "--shallow_since" can have a
format like "1551301058 -0500" this argument needs to be quoted.
Do so. This could go unnoticed, as the git_repository rule always
falls back to full cloning; nevertheless, having shallow clones
not working can be a huge performance impact.

Change-Id: I853c128cc6413d6cb314277dbfd04c98c17f07b5
PiperOrigin-RevId: 236850530

bazelbuild/bazel,aehlig/bazel,werkt/bazel,safarmer/bazel,meteorcloudy/bazel,perezd/bazel,ButterflyNetwork/bazel,twitter-forks/bazel,dslomov/bazel,safarmer/bazel,davidzchen/bazel,ButterflyNetwork/bazel,dslomov/bazel,werkt/bazel,cushon/bazel,ulfjack/bazel,akira-baruah/bazel,dslomov/bazel-windows,twitter-forks/bazel,perezd/bazel,ulfjack/bazel,werkt/bazel,katre/bazel,cushon/bazel,katre/bazel,akira-baruah/bazel,dslomov/bazel-windows,cushon/bazel,twitter-forks/bazel,davidzchen/bazel,ButterflyNetwork/bazel,akira-baruah/bazel,bazelbuild/bazel,dslomov/bazel-windows,bazelbuild/bazel,dslomov/bazel,safarmer/bazel,aehlig/bazel,cushon/bazel,safarmer/bazel,meteorcloudy/bazel,akira-baruah/bazel,katre/bazel,davidzchen/bazel,dslomov/bazel-windows,meteorcloudy/bazel,aehlig/bazel,twitter-forks/bazel,aehlig/bazel,dslomov/bazel,akira-baruah/bazel,katre/bazel,twitter-forks/bazel,safarmer/bazel,safarmer/bazel,bazelbuild/bazel,werkt/bazel,ulfjack/bazel,bazelbuild/bazel,aehlig/bazel,bazelbuild/bazel,aehlig/bazel,werkt/bazel,ButterflyNetwork/bazel,perezd/bazel,meteorcloudy/bazel,cushon/bazel,ButterflyNetwork/bazel,katre/bazel,ulfjack/bazel,meteorcloudy/bazel,perezd/bazel,dslomov/bazel,werkt/bazel,davidzchen/bazel,ulfjack/bazel,akira-baruah/bazel,dslomov/bazel-windows,meteorcloudy/bazel,davidzchen/bazel,twitter-forks/bazel,perezd/bazel,meteorcloudy/bazel,perezd/bazel,ButterflyNetwork/bazel,ulfjack/bazel,dslomov/bazel,aehlig/bazel,dslomov/bazel,twitter-forks/bazel,katre/bazel,dslomov/bazel-windows,davidzchen/bazel,ulfjack/bazel,davidzchen/bazel,perezd/bazel,cushon/bazel