chore: regenerate README (#676)

This PR was generated using Autosynth. 🌈


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

```
2021-06-25 23:41:12,796 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-firestore/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-25 23:41:14,066 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

Full log will be available here:
https://source.cloud.google.com/results/invocations/28f0e2fc-4f38-4e5c-8bc2-4b19dbb52f6c/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-firestore.git",
-        "sha": "abf03fd06d4f77582c2ad24b8721b3c3556bdef1"
+        "sha": "969f7fd72b07aa9c916609b73528ff0f17dfaead"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "2430f8d90ed8a508e8422a3a7191e656d5a6bf53"
+        "sha": "157678ee74b6ee0d954023ea7450a9c1d5a5743f"
       }
     }
   ]

README.md

@@ -45,18 +45,18 @@ If you are using Maven without BOM, add this to your dependencies:
 
 If you are using Gradle 5.x or later, add this to your dependencies
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:20.6.0')
+implementation platform('com.google.cloud:libraries-bom:20.7.0')
 
 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:2.5.0'
+compile 'com.google.cloud:google-cloud-firestore:2.5.1'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-firestore" % "2.5.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-firestore" % "2.5.1"
 ```
 
 ## Authentication