chore: regenerate README (#585)

This PR was generated using Autosynth. 🌈


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

```
2021-05-26 21:03:21,772 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-containeranalysis/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-26 21:03:23,104 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/d94956e3-a693-41db-bb3c-ad3d155952e7/targets

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Author: yoshi-automation

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-containeranalysis.git",
-        "sha": "89ae39104d79869e030b4729c93e17f35d5963ff"
+        "sha": "8c19825cd2960db6565002b32f6782dd8f1a4f0c"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "a2de127f90799cd5bace653b1dcc5dd2ca8b19c9"
+        "sha": "1778de119522ea9c9b18763c2a4577e22a60433c"
       }
     }
   ]

README.md

@@ -51,12 +51,12 @@ compile 'com.google.cloud:google-cloud-containeranalysis'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-containeranalysis:1.3.0'
+compile 'com.google.cloud:google-cloud-containeranalysis:1.3.1'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-containeranalysis" % "1.3.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-containeranalysis" % "1.3.1"
 ```
 
 ## Authentication