chore: regenerate README (#551)

This PR was generated using Autosynth. 🌈


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

```
2021-05-13 14:04:56,227 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-dialogflow/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-13 14:04:57,884 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/81e22696-d0b8-4734-a347-5b507efb1853/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-dialogflow.git",
-        "sha": "c9a518870f51e5ffde16671cbc09b11a3bfdc3e0"
+        "sha": "0e0d5a3011f00880e0f2b0214932f434babe5750"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "6726988c677bb78385868bfc48dbfa2fe981d44a"
+        "sha": "bd8281a06cc7f84906e04d4843c1d3d386a980cd"
       }
     }
   ]

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>20.3.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>