chore(deps): bump flyway-core from 6.3.1 to 6.4.0 (#787)

Bumps [flyway-core](https://github.com/flyway/flyway) from 6.3.1 to 6.4.0.
- [Release notes](https://github.com/flyway/flyway/releases)
- [Commits](https://github.com/flyway/flyway/compare/flyway-6.3.1...flyway-6.4.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

build.gradle

@@ -66,7 +66,7 @@ ext {
     flexmarkVersion =  "0.61.20"
     thumbnailatorVersion =  "0.4.11"
     image4jVersion =  "0.7zensight1"
-    flywayVersion =  "6.3.1"
+    flywayVersion =  "6.4.0"
     h2Version =  "1.4.196"
     levelDbVersion =  "0.12"
     jsonVersion =  "20190722"