chore: regenerate README (#543)

This PR was generated using Autosynth. 🌈


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

```
2021-05-11 23:44:18,951 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-monitoring/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-11 23:44:20,290 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/43178721-2cc7-43fa-9131-7fd0780e1454/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-monitoring.git",
-        "sha": "8f07c54c78046b30f7dfd49ddf54ba932db7787d"
+        "sha": "3c9cb79ebd0e17e96b3c1577e83fec5ddc567de8"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "6726988c677bb78385868bfc48dbfa2fe981d44a"
+        "sha": "f7e7449a641ce47f2a04ed577dec48e109325e76"
       }
     }
   ]

README.md

@@ -17,7 +17,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>20.2.0</version>
+      <version>20.3.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -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>2.2.1</version>
+  <version>2.2.2-SNAPSHOT</version>
 </dependency>
 
 ```