chore: regenerate README (#549)

This PR was generated using Autosynth. 🌈


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

```
2021-05-13 23:43:12,620 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-monitoring/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-13 23:43:13,904 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/feb8e9a5-d7ee-472c-ae6a-cb25f4dacd25/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-monitoring.git",
-        "sha": "488f2f755d19168a3ad70114300f48b6744a0f5f"
+        "sha": "75270a7cea1cda16bfd8ef3ccc1b4a2673b239eb"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "f7e7449a641ce47f2a04ed577dec48e109325e76"
+        "sha": "4f4b1b9b8d8b52f1e9e4a76165896debce5ab7f1"
       }
     }
   ]

README.md

@@ -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:2.2.1'
+compile 'com.google.cloud:google-cloud-monitoring:2.2.2'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-monitoring" % "2.2.1"
+libraryDependencies += "com.google.cloud" % "google-cloud-monitoring" % "2.2.2"
 ```
 
 ## Authentication