chore(deps): update dependency google-cloud-spanner to v1.18.0 (GoogleCloudPlatform#4563)

Co-authored-by: Dina Graves Portman <[email protected]>

Author: renovate-bot

appengine/standard_python3/spanner/requirements.txt

@@ -1,2 +1,2 @@
-google-cloud-spanner==1.17.1
+google-cloud-spanner==1.18.0
 Flask==1.1.2

functions/spanner/requirements.txt

@@ -1 +1 @@
-google-cloud-spanner==1.17.1
+google-cloud-spanner==1.18.0

spanner/cloud-client/requirements.txt

@@ -1,2 +1,2 @@
-google-cloud-spanner==1.17.1
+google-cloud-spanner==1.18.0
 futures==3.3.0; python_version < "3"