chore: regenerate README (#658)

This PR was generated using Autosynth. 🌈


<details><summary>Log from Synthtool</summary>

```
2021-06-02 20:44:35,874 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-firestore/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-02 20:44:37,196 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

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.github/readme/synth.metadata/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-firestore.git",
-        "sha": "4259bb218f2dd3edbdfb3271bbcd361d45b5e064"
+        "sha": "b93ca8a2b5751c61b3fbe0ca608056e2c0398575"
       }
     },
     {

README.md

@@ -51,12 +51,12 @@ compile 'com.google.cloud:google-cloud-firestore'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-firestore:2.4.0'
+compile 'com.google.cloud:google-cloud-firestore:2.5.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-firestore" % "2.4.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-firestore" % "2.5.0"
 ```
 
 ## Authentication