chore(java): allow overriding the versioning section of the Java README (#495) (#125)

Allows setting a `versioning` section in `.readme-partials.yaml` to override the versioning section.

Source-Author: Jeff Ching <chingor@google.com>
Source-Date: Fri Apr 17 10:04:04 2020 -0700
Source-Repo: googleapis/synthtool
Source-Sha: f8a9933e5e98202b04ef427f28d1d79221190fa4
Source-Link: googleapis/synthtool@f8a9933

Author: yoshi-automation

README.md

@@ -133,8 +133,8 @@ Java 7 or above is required for using this client.
 
 ## Versioning
 
-This library follows [Semantic Versioning](http://semver.org/).
 
+This library follows [Semantic Versioning](http://semver.org/).
 
 
 ## Contributing

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-language.git",
-        "sha": "a67ee0a792da7fa84f058b451445144db06d9e9e"
+        "sha": "c1f493bce0f3e500b60834d115656a292a18e55c"
       }
     },
     {
@@ -27,7 +27,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "52638600f387deb98efb5f9c85fec39e82aa9052"
+        "sha": "f8a9933e5e98202b04ef427f28d1d79221190fa4"
       }
     }
   ],