Update handlebars requirement from 2.0.0-beta.2 to 3.0.0

Updates the requirements on [handlebars](https://github.com/sunng87/handlebars-rust) to permit the latest version.
- [Release notes](https://github.com/sunng87/handlebars-rust/releases)
- [Changelog](https://github.com/sunng87/handlebars-rust/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sunng87/handlebars-rust/compare/handlebars-2.0.0-beta.2...v3.0.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

acmed/Cargo.toml

@@ -15,7 +15,7 @@ publish = false
 [dependencies]
 acme_common = { path = "../acme_common" }
 clap = "2.32"
-handlebars = "2.0.0-beta.2"
+handlebars = "3.0.0"
 http_req = "0.5"
 log = "0.4"
 nom = "5.0"