Post release library version increment to 0.18.21 (from 0.18.20)

Author: ViliusSutkus89

build.gradle

@@ -9,7 +9,7 @@ task clean(type: Delete) {
 }
 
 group = 'com.viliussutkus89'
-version = '0.18.20'
+version = '0.18.21'
 
 nexusPublishing {
     repositories {