Add edition manifest key

Author: krtab

Cargo.toml

@@ -10,6 +10,7 @@ documentation = "https://docs.rs/rustc-demangle"
 description = """
 Rust compiler symbol demangling.
 """
+edition = "2015"
 
 [workspace]
 members = ["crates/capi", "fuzz"]

crates/capi/Cargo.toml

@@ -7,6 +7,7 @@ C API for the `rustc-demangle` crate
 """
 license = "MIT/Apache-2.0"
 repository = "https://github.com/alexcrichton/rustc-demangle"
+edition = "2015"
 
 [lib]
 name = "rustc_demangle"

crates/native-c/Cargo.toml

@@ -7,6 +7,7 @@ Native C version of the rustc_demangle crate
 """
 license = "MIT/Apache-2.0"
 repository = "https://github.com/rust-lang/rustc-demangle"
+edition = "2015"
 
 [lib]
 name = "rustc_demangle_native_c"