Bump fluent-bundle from 0.6.0 to 0.15.0

Bumps [fluent-bundle](https://github.com/projectfluent/fluent-rs) from 0.6.0 to 0.15.0.
- [Release notes](https://github.com/projectfluent/fluent-rs/releases)
- [Commits](https://github.com/projectfluent/fluent-rs/compare/[email protected]@0.15.0)

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

Author: dependabot-preview[bot]

Cargo.lock

@@ -7,7 +7,7 @@ edition = "2018"
 [dependencies]
 lazy_static = "1.2.0"
 fluent = "0.16"
-fluent-bundle = "0.6.0"
+fluent-bundle = "0.15.0"
 fluent-syntax = "0.11.0"
 fluent-locale = "0.10.1"
 handlebars-fluent = "0.2.0"