Bump annotations from 20.1.0 to 21.0.1 in /modules/postgresql

Bumps [annotations](https://github.com/JetBrains/java-annotations) from 20.1.0 to 21.0.1.
- [Release notes](https://github.com/JetBrains/java-annotations/releases)
- [Changelog](https://github.com/JetBrains/java-annotations/blob/master/CHANGELOG.md)
- [Commits](JetBrains/java-annotations@20.1.0...21.0.1)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

modules/postgresql/build.gradle

@@ -16,5 +16,5 @@ dependencies {
     testCompile testFixtures(project(':r2dbc'))
     testCompile 'io.r2dbc:r2dbc-postgresql:0.8.5.RELEASE'
 
-    compileOnly 'org.jetbrains:annotations:20.1.0'
+    compileOnly 'org.jetbrains:annotations:21.0.1'
 }