Fix license field for lambda_runtime (#302)

The license field for lambda_runtime was not using the correct
identifier preventing publishing to crates.io.

Author: bahildebrand

lambda-runtime/Cargo.toml

@@ -4,7 +4,7 @@ version = "0.3.0"
 authors = ["David Barsky <[email protected]>"]
 description = "AWS Lambda Runtime"
 edition = "2018"
-license = "Apache License 2.0"
+license = "Apache-2.0"
 repository = "https://github.com/awslabs/aws-lambda-rust-runtime"
 categories = ["web-programming::http-server"]
 keywords = ["AWS", "Lambda", "API"]