Add shallow_since to WORKSPACE git_repository rules

per bazel warning
DEBUG: Rule 'com_apt_itude_rules_pip' indicated that a canonical reproducible form can be obtained by modifying arguments shallow_since = "1564255337 -0400"

Change-Id: I6564e8325aa31bbd156ffdf85854f3f5459bd4df
diff --git a/WORKSPACE b/WORKSPACE
index 46c58c4..d3079bf 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -80,6 +80,7 @@
     name = "com_apt_itude_rules_pip",
     commit = "186bade4f054c0a9be7037585584c9c572cba483",
     remote = "https://github.com/apt-itude/rules_pip.git",
+    shallow_since = "1564255337 -0400"
 )
 
 # Python dependencies
@@ -125,6 +126,7 @@
     name = "com_googlesource_gerrit_bazlets",
     remote = "https://gerrit.googlesource.com/bazlets",
     commit = "1d381f01c853e2c02ae35430a8e294e485635d62",
+    shallow_since = "1559431096 -0400"
 )
 
 load("@com_googlesource_gerrit_bazlets//:gerrit_api.bzl", "gerrit_api")
@@ -249,6 +251,7 @@
     name = "com_googlesource_gerrit_plugin_owners",
     remote = "https://gerrit.googlesource.com/plugins/owners/",
     commit = "5e691e87b8c00a04d261a8dd313f4d16c54797e8",
+    shallow_since = "1559729722 +0900"
 )
 
 # Go image repos for Docker