chore: regenerate README (#412)

This PR was generated using Autosynth. 🌈


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

```
2021-01-12 12:18:05,674 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-dialogflow/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-01-12 12:18:06,637 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/85fdfc70-1135-4808-ae60-03272cb69660/targets

- [ ] To automatically regenerate this PR, check this box.

Author: yoshi-automation

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-dialogflow.git",
-        "sha": "11e24ee8a8eabad638fd3edd3c17461cfea8f83b"
+        "sha": "84b99f450e10e0d1f9468e7e32c3c4ad7c89854b"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "996775eca5fd934edac3c2ae34b80ff0395b1717"
+        "sha": "16ec872dd898d7de6e1822badfac32484b5d9031"
       }
     }
   ]

README.md

@@ -38,18 +38,25 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-dialogflow</artifactId>
-  <version>2.4.3</version>
+  <version>2.4.5</version>
 </dependency>
 
 ```
 
-If you are using Gradle, add this to your dependencies
+If you are using Gradle 5.x or later, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-dialogflow:2.4.3'
+implementation platform('com.google.cloud:libraries-bom:16.2.1')
+
+compile 'com.google.cloud:google-cloud-dialogflow'
+```
+If you are using Gradle without BOM, add this to your dependencies
+```Groovy
+compile 'com.google.cloud:google-cloud-dialogflow:2.4.5'
 ```
+
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-dialogflow" % "2.4.3"
+libraryDependencies += "com.google.cloud" % "google-cloud-dialogflow" % "2.4.5"
 ```
 
 ## Authentication