chore: regenerate README (#551)

This PR was generated using Autosynth. 🌈


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

```
2021-05-17 01:51:49,255 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-dataproc/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-17 01:51:50,499 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/1e40a6b3-5492-4340-a2d7-fc51dbf4353a/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-dataproc.git",
-        "sha": "1436c71b3d4ba310adfccc79b1edee1a37194eb3"
+        "sha": "dba5c00ea398ccc1fd5ff4b7f6edfc47988ba514"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "6726988c677bb78385868bfc48dbfa2fe981d44a"
+        "sha": "4f4b1b9b8d8b52f1e9e4a76165896debce5ab7f1"
       }
     }
   ]

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>20.2.0</version>
+      <version>20.4.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -46,18 +46,18 @@ 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:20.3.0')
+implementation platform('com.google.cloud:libraries-bom:20.4.0')
 
 compile 'com.google.cloud:google-cloud-dataproc'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-dataproc:1.4.2'
+compile 'com.google.cloud:google-cloud-dataproc:1.4.3'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-dataproc" % "1.4.2"
+libraryDependencies += "com.google.cloud" % "google-cloud-dataproc" % "1.4.3"
 ```
 
 ## Authentication