chore: regenerate README (#650)

This PR was generated using Autosynth. 🌈


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

```
2021-08-09 19:36:19,845 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-containeranalysis/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-09 19:36:21,102 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/75845cf3-b67c-430d-bb59-f1fa0d9abc07/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-containeranalysis.git",
-        "sha": "fa8c7a4243499b37fb065aae1e7b75f147c35129"
+        "sha": "0baa2032b64f6c92f9ed80d05addd25823928dc4"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "3d32990b6f4b57be77455e3ca89e6e21cd0c06b3"
+        "sha": "5605f38f153e7627ba4441a2c5181060b664d224"
       }
     }
   ]

README.md

@@ -41,7 +41,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-containeranalysis</artifactId>
-  <version>1.3.5</version>
+  <version>1.4.0</version>
 </dependency>
 
 ```
@@ -56,13 +56,13 @@ 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:1.3.5'
+compile 'com.google.cloud:google-cloud-containeranalysis:1.4.0'
 ```
 
 If you are using SBT, add this to your dependencies
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-containeranalysis" % "1.3.5"
+libraryDependencies += "com.google.cloud" % "google-cloud-containeranalysis" % "1.4.0"
 ```
 
 ## Authentication