chore: regenerate README (#406)

This PR was generated using Autosynth. 🌈


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

```
2021-02-10 16:08:34,948 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-containeranalysis/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-02-10 16:08:35,868 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/8230f17c-ef73-4f1d-8975-33c786a2b58b/targets

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

Author: yoshi-automation

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-containeranalysis.git",
-        "sha": "f7d44075a3ea3cd0bb2e760357c229698ff40fe1"
+        "sha": "c7da905c9252220a9ae38d78d6cb393a2a42f0ce"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "e935c9ecb47da0f2e054f5f1845f7cf7c95fa625"
+        "sha": "2414b817065726eae0bc525346c7e874f969369d"
       }
     }
   ]

README.md

@@ -17,7 +17,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>16.3.0</version>
+      <version>16.4.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -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-containeranalysis'
 ```