chore: regenerate README (#515)

This PR was generated using Autosynth. 🌈


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

```
2021-08-19 17:27:50,362 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-iamcredentials/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-19 17:27:51,928 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/b2b1c50c-8c11-4da2-81c9-c7e640e7aa30/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-iamcredentials.git",
-        "sha": "a4bd6ebc8979683f393f5957a586b96a581dced2"
+        "sha": "6a92626f5b2877b0415540413a5df29a0af94082"
       }
     },
     {

README.md

@@ -41,7 +41,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-iamcredentials</artifactId>
-  <version>1.3.2</version>
+  <version>2.0.1</version>
 </dependency>
 
 ```