Update README.md

[ci skip]

Author: overheadhunter

README.md

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 # RFC 5297 SIV mode of operation in Java
 
-[![Build Status](https://travis-ci.org/cryptomator/siv-mode.svg?branch=master)](https://travis-ci.org/cryptomator/siv-mode)
+[![Build Status](https://travis-ci.org/cryptomator/siv-mode.svg?branch=develop)](https://travis-ci.org/cryptomator/siv-mode)
 [![Codacy Badge](https://api.codacy.com/project/badge/Grade/8b274788dab046259a40e56688236790)](https://www.codacy.com/app/cryptomator/siv-mode)
 [![Codacy Badge](https://api.codacy.com/project/badge/Coverage/8b274788dab046259a40e56688236790)](https://www.codacy.com/app/cryptomator/siv-mode)
 [![Coverity Scan Build Status](https://scan.coverity.com/projects/10005/badge.svg)](https://scan.coverity.com/projects/cryptomator-siv-mode)