chore: regenerate README (#629)

This PR was generated using Autosynth. 🌈


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

```
2020-11-16 09:39:34,370 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-spanner/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working directory clean
2020-11-16 09:39:35,372 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/9791673c-003a-4905-b9e9-82823cf86535/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-spanner.git",
-        "sha": "5be4d9cc62422120e24ecc25fd9f2d14500f0ad5"
+        "sha": "9ff50fb018017d8d1eea6be7986d8c88bcce0ed3"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "e89175cf074dccc4babb4eca66ae913696e47a71"
+        "sha": "d5fc0bcf9ea9789c5b0e3154a9e3b29e5cea6116"
       }
     }
   ]

README.md

@@ -45,11 +45,11 @@ If you are using Maven without BOM, add this to your dependencies:
 
 If you are using Gradle, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-spanner:3.0.1'
+compile 'com.google.cloud:google-cloud-spanner:3.0.2'
 ```
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "3.0.1"
+libraryDependencies += "com.google.cloud" % "google-cloud-spanner" % "3.0.2"
 ```
 
 ## Authentication