chore: regenerate README (#571)

This PR was generated using Autosynth. 🌈


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

```
2021-06-03 00:25:18,017 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-dataproc/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-03 00:25:19,230 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/ebb26191-0435-46b9-89d0-10b1f0082d56/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": "8199bda638bb86aa16abb5122bb563a909a76601"
+        "sha": "f18a46eb06a2998113a6f09ed2262a5a28af221e"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "c3e41da0fa256ad7f6b4bc76b9d069dedecdfef4"
+        "sha": "811d20bc0b00c09773dfc74ac2baaf1286e943b7"
       }
     }
   ]

README.md

@@ -39,7 +39,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-dataproc</artifactId>
-  <version>1.5.0</version>
+  <version>1.5.1</version>
 </dependency>
 
 ```
@@ -52,12 +52,12 @@ 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:1.5.0'
+compile 'com.google.cloud:google-cloud-dataproc:1.5.1'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-dataproc" % "1.5.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-dataproc" % "1.5.1"
 ```
 
 ## Authentication