all: reduce go requirement from 1.13 to 1.9

(1.13 is the default, which is why it was there, but in reality we target 1.9+)

Change-Id: I6f8dd1e965121ac4cb97181a9a810bc36fe74e7e
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/45451
Reviewed-by: Chris Broadfoot <cbro@google.com>
diff --git a/firestore/go.mod b/firestore/go.mod
index 20660e5..2639cbc 100644
--- a/firestore/go.mod
+++ b/firestore/go.mod
@@ -1,6 +1,6 @@
 module cloud.google.com/go/firestore
 
-go 1.13
+go 1.9
 
 require (
 	cloud.google.com/go v0.46.1
diff --git a/pubsub/go.mod b/pubsub/go.mod
index a5567f7..3ddf04f 100644
--- a/pubsub/go.mod
+++ b/pubsub/go.mod
@@ -1,6 +1,6 @@
 module cloud.google.com/go/pubsub
 
-go 1.13
+go 1.9
 
 require (
 	cloud.google.com/go v0.45.1