Update bigdecimal requirement from 0.1 to 0.2 (apache#268)

Updates the requirements on [bigdecimal](https://github.com/akubera/bigdecimal-rs) to permit the latest version.
- [Release notes](https://github.com/akubera/bigdecimal-rs/releases)
- [Commits](akubera/bigdecimal-rs@v0.1.0...v0.2.0)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Cargo.toml

@@ -23,7 +23,7 @@ path = "src/lib.rs"
 json_example = ["serde_json", "serde"]
 
 [dependencies]
-bigdecimal = { version = "0.1", features = ["serde"], optional = true }
+bigdecimal = { version = "0.2", features = ["serde"], optional = true }
 log = "0.4"
 serde = { version = "1.0", features = ["derive"], optional = true }
 # serde_json is only used in examples/cli, but we have to put it outside