Bump bifurcan from 0.2.0-alpha4 to 0.2.0-alpha6

Bumps [bifurcan](https://github.com/lacuna/bifurcan) from 0.2.0-alpha4 to 0.2.0-alpha6.
- [Release notes](https://github.com/lacuna/bifurcan/releases)
- [Changelog](https://github.com/lacuna/bifurcan/blob/master/CHANGELOG.md)
- [Commits](lacuna/bifurcan@0.2.0-alpha4...0.2.0-alpha6)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

exist-parent/pom.xml

@@ -420,7 +420,7 @@
             <dependency>
                 <groupId>io.lacuna</groupId>
                 <artifactId>bifurcan</artifactId>
-                <version>0.2.0-alpha4</version>
+                <version>0.2.0-alpha6</version>
             </dependency>
 
             <dependency>