Edited 07.12.2018:
I think dependency for StringUtils you are using is not proper.
Please add below dependency to gradle and Sync project and import your class.
implementation 'org.apache.commons:commons-lang3:3.6'
This on is using deprecated task (but should still works):
compile ‘org.apache.commons:commons-lang3:3.5’
Edit:
As OoDeLally mentioned in a comment,
Above mentioned version is deprecated,
Please use below dependency:
implementation 'org.apache.commons:commons-text:1.9'
Edit 2:
deprecated as for July 2019. Use stackoverflow.com/a/55567755/1541141 instead
Thanks @OoDeLally!