chore: regenerate README (#363)

This PR was generated using Autosynth. 🌈


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

```
2021-02-09 17:36:09,876 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-websecurityscanner/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-02-09 17:36:10,755 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/f8d159f6-dbf5-43f0-9a97-14a4566d867a/targets

- [ ] To automatically regenerate this PR, check this box.

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-websecurityscanner.git",
-        "sha": "88c429946a210e3c843156c6394b97b52564580b"
+        "sha": "39acca94e0c6c5849cff86fdcafe5cba98da6de3"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "692715c0f23a7bb3bfbbaa300f7620ddfa8c47e5"
+        "sha": "4679e7e415221f03ff2a71e3ffad75b9ec41d87e"
       }
     }
   ]

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:16.3.0')
+implementation platform('com.google.cloud:libraries-bom:16.4.0')
 
 compile 'com.google.cloud:google-cloud-websecurityscanner'
 ```