chore: regenerate README (#566)

This PR was generated using Autosynth. 🌈


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

```
2021-06-23 16:05:56,309 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-logging/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-23 16:05:57,574 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/92fe427b-1027-4e37-a150-bd0113c016fd/targets

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

Author: yoshi-automation

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-logging.git",
-        "sha": "a83274939ad3bad457003cb557327abe280080c3"
+        "sha": "5a5f7371569f3e5656a3e40fcc2d72b7a8e0e916"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "740366bbb9a7e0f4b77fc75dc26be1d3a376c3e0"
+        "sha": "9763f20e4b7bb1091082462b2f7970e965d0d414"
       }
     }
   ]

README.md

@@ -46,7 +46,7 @@ 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:20.6.0')
+implementation platform('com.google.cloud:libraries-bom:20.7.0')
 
 compile 'com.google.cloud:google-cloud-logging'
 ```