Upgrade patch version number

Signed-off-by: Jarno Elovirta <jarno@elovirta.com>

Author: jelovirt

build.gradle

@@ -5,7 +5,7 @@ sourceCompatibility = 11
 targetCompatibility = 11
 
 group = 'com.elovirta.dita'
-version = "5.9.0"
+version = "5.9.1"
 
 repositories {
     mavenCentral()