Bump minimum 'api_core' version for all GAPIC libs to 1.4.1. (#6391)

Closes #6390.

Author: tseaver

setup.py

@@ -29,18 +29,18 @@
 # 'Development Status :: 5 - Production/Stable'
 release_status = 'Development Status :: 5 - Production/Stable'
 dependencies = [
-    'googleapis-common-protos<2.0dev,>=1.5.3,!=1.5.4',
-    'protobuf>=3.4.0',
-    'google-auth<2.0.0dev,>=0.4.0',
-    'requests<3.0.0dev,>=2.18.0',
-    'setuptools>=34.0.0',
-    'six>=1.10.0',
+    'googleapis-common-protos >= 1.5.3, != 1.5.4, < 2.0dev',
+    'protobuf >= 3.4.0',
+    'google-auth >= 0.4.0, < 2.0dev',
+    'requests >= 2.18.0, < 3.0.0dev',
+    'setuptools >= 34.0.0',
+    'six >= 1.10.0',
     'pytz',
-    'futures>=3.2.0;python_version<"3.2"'
+    'futures >= 3.2.0; python_version < "3.2"'
 ]
 extras = {
-    'grpc': 'grpcio>=1.8.2',
-    'grpcio-gcp': 'grpcio-gcp>=0.2.2'
+    'grpc': 'grpcio >= 1.8.2',
+    'grpcio-gcp': 'grpcio-gcp >= 0.2.2'
 }