(maint) unpin puppetlabs-postgresql, allow 10.x versions

This removes the pin for the version of puppetlabs-postgresql in `.fixtures.yaml`
and also updates the metadata to indicate that the current major version of
`puppetlabs-postgresql` is supported.

.fixtures.yml

@@ -14,9 +14,7 @@ fixtures:
     augeas_core: 'https://github.com/puppetlabs/puppetlabs-augeas_core.git'
     postgresql: 'https://github.com/puppetlabs/puppetlabs-postgresql.git'
     firewall: 'https://github.com/puppetlabs/puppetlabs-firewall.git'
-    postgresql:
-      repo: 'https://github.com/puppetlabs/puppetlabs-postgresql.git'
-      ref: 'v9.2.0'
+    postgresql: 'https://github.com/puppetlabs/puppetlabs-postgresql.git'
     firewall: 'https://github.com/puppetlabs/puppetlabs-firewall.git'
   symlinks:
     puppetdb: '#{source_dir}'

metadata.json

@@ -14,7 +14,7 @@
     },
     {
       "name": "puppetlabs/postgresql",
-      "version_requirement": ">= 6.5.0 < 10.0.0"
+      "version_requirement": ">= 6.5.0 < 11.0.0"
     },
     {
       "name": "puppetlabs/firewall",