Add "rust-version" field

Cargo.toml

@@ -3,15 +3,16 @@ name = "os_str_bytes"
 version = "4.2.0"
 authors = ["dylni"]
 edition = "2018"
-exclude = [".*", "/rustfmt.toml", "/tests"]
+rust-version = "1.51.0"
 description = """
 Utilities for converting between byte sequences and platform-native strings
 """
-repository = "https://github.com/dylni/os_str_bytes"
 readme = "README.md"
+repository = "https://github.com/dylni/os_str_bytes"
+license = "MIT OR Apache-2.0"
 keywords = ["bytes", "osstr", "osstring", "path", "windows"]
 categories = ["command-line-interface", "development-tools::ffi", "encoding", "os", "rust-patterns"]
-license = "MIT OR Apache-2.0"
+exclude = [".*", "/rustfmt.toml", "/tests"]
 
 [package.metadata.docs.rs]
 all-features = true