chore: regenerate README (#487)

This PR was generated using Autosynth. 🌈


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

```
2021-04-12 23:46:14,326 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-monitoring/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-12 23:46:15,585 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/c4deb9f8-4e82-4efa-a242-8101b9bc1c2e/targets

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

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-monitoring.git",
-        "sha": "f047185838aa5fb4a80e43354f0d34b313821339"
+        "sha": "369073202f2fc389567a742cb5f897724d5d33c2"
       }
     },
     {

README.md

@@ -39,7 +39,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-monitoring</artifactId>
-  <version>2.2.0</version>
+  <version>2.2.1-SNAPSHOT</version>
 </dependency>
 
 ```
@@ -52,12 +52,12 @@ compile 'com.google.cloud:google-cloud-monitoring'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-monitoring:2.1.0'
+compile 'com.google.cloud:google-cloud-monitoring:2.2.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-monitoring" % "2.1.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-monitoring" % "2.2.0"
 ```
 
 ## Authentication