chore: regenerate README (#420)

This PR was generated using Autosynth. 🌈


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

```
2021-05-26 21:02:07,005 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-redis/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-26 21:02:08,120 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/adcabd9a-abd0-4782-b166-1fbee5777f9a/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-redis.git",
-        "sha": "ec0092cf61fe8914c065818857e3fca525cb76f4"
+        "sha": "e9a64bce19b7fd59f19655b7d5b44de0ed1786f3"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "7332178a11ddddc91188dc0f25bca1ccadcaa6c6"
+        "sha": "1778de119522ea9c9b18763c2a4577e22a60433c"
       }
     }
   ]

README.md

@@ -45,7 +45,7 @@ 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:20.4.0')
+implementation platform('com.google.cloud:libraries-bom:20.5.0')
 
 compile 'com.google.cloud:google-cloud-redis'
 ```