ensure pip_compile_requirements py_binary target can recieve 'tags' (#496)

python/pip_install/requirements.bzl

diff --git a/python/pip_install/requirements.bzl b/python/pip_install/requirements.bzl
index 55e8f61..a21f13a 100644
--- a/python/pip_install/requirements.bzl
+++ b/python/pip_install/requirements.bzl
@@ -9,6 +9,7 @@
         visibility = ["//visibility:private"],
         requirements_in = None,
         requirements_txt = None,
+        tags = None,
         **kwargs):
     """
     Macro creating targets for running pip-compile
@@ -28,6 +29,7 @@
         visibility: passed to both the _test and .update rules
         requirements_in: file expressing desired dependencies
         requirements_txt: result of "compiling" the requirements.in file
+        tags: tagging attribute common to all build rules, passed to both the _test and .update rules
         **kwargs: other bazel attributes passed to the "_test" rule
     """
     requirements_in = name + ".in" if requirements_in == None else requirements_in
@@ -69,6 +71,7 @@
         "deps": deps,
         "main": pip_compile,
         "srcs": [pip_compile],
+        "tags": tags,
         "visibility": visibility,
     }