Making **explicit** datastore and spanner dependency on api-core changes.

Author: dhermes

datastore/setup.py

@@ -52,7 +52,7 @@
 
 REQUIREMENTS = [
     'google-cloud-core >= 0.28.0, < 0.29dev',
-    'google-api-core >= 0.1.1, < 0.2.0dev',
+    'google-api-core >= 0.1.5.dev1, < 0.2.0dev',
     'google-auth >= 1.0.2, < 2.0dev',
     'google-gax >= 0.15.15, < 0.16dev',
     'googleapis-common-protos[grpc] >= 1.5.2, < 2.0dev',

spanner/setup.py

@@ -53,7 +53,7 @@
 REQUIREMENTS = [
     'google-auth >= 1.1.0',
     'google-cloud-core[grpc] >= 0.28.0, < 0.29dev',
-    'google-api-core >= 0.1.4, < 0.2.0dev',
+    'google-api-core >= 0.1.5.dev1, < 0.2.0dev',
     'grpc-google-iam-v1 >= 0.11.4, < 0.12dev',
     'requests >= 2.18.4, < 3.0dev',
 ]