added CHANGELOG for 6.0.4

CHANGELOG.md

+### 6.0.4
+
+- Added styleci config, add styleci-php-cs bridge to check formatting
+- Removed composer.lock
+- Fix: 'iat' added to payload should be always an int
+- Fix #34: strlen() and substr() can misbehave with mbstring.func_overload
+- Fix: Don't cast to boolean the result of openssl_verify()
+
+### 6.x.x - Not Backwards Compatible
+
+- Dropped support for PHP 5.3
+- Don't escape slashes when generating signin input.
+  This may render tokens generated with earlier versions of Jose incompatible.
+- **DON'T** install version 6.0.2! It's using phpseclib version 2 instead of version 1 and some classes are broken
+
+### 3.x.x to 4.x.x - Not Backwards Compatible
+
+Added the ability to set custom properties in the header. Moved automatic inclusion of certain claims into an SimpleJWS class from the base JWS class.
+
+### 2.x.x to 3.x.x
+
+Introduced the ability to specify an encryption engine. Added support of PHPSecLib to the existing OpenSSL implementation.
+