chore: regenerate README (#358)

This PR was generated using Autosynth. 🌈


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

```
2021-02-17 00:23:36,788 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-spanner-jdbc/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-02-17 00:23:38,272 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/05814b29-71ca-4400-9962-ee9d469b6688/targets

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

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-spanner-jdbc.git",
-        "sha": "8b4e50d10a9121334be3d8b5ed0d8fc9ff63c182"
+        "sha": "653de1642291e60f0b28de0d1332b6504b7a9274"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "d1bb9173100f62c0cfc8f3138b62241e7f47ca6a"
+        "sha": "f327d3b657a63ae4a8efd7f011a15eacae36b59c"
       }
     }
   ]

README.md

@@ -17,18 +17,18 @@ If you are using Maven, add this to your pom.xml file:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-spanner-jdbc</artifactId>
-  <version>1.18.3</version>
+  <version>1.19.0</version>
 </dependency>
 ```
 
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-spanner-jdbc:1.18.3'
+compile 'com.google.cloud:google-cloud-spanner-jdbc:1.19.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-spanner-jdbc" % "1.18.3"
+libraryDependencies += "com.google.cloud" % "google-cloud-spanner-jdbc" % "1.19.0"
 ```
 
 ## Authentication