Fixes unreachable! calls in Rust 1.59+ (#21)

Starting in Rust 1.59, calls to the `unreachable!` macro no longer
accept string variables as their first parameter. This brings their
behavior in line with macros like `println!`, `format!`, and `write!`.

See: rust-lang/rust#94475

src/bin/ion/commands/beta/mod.rs

@@ -39,7 +39,7 @@ pub fn run(_command_name: &str, matches: &ArgMatches<'static>) -> Result<()> {
             "The requested beta command ('{}') is not supported and clap did not generate an error message.",
             command_name
         );
-        unreachable!(message);
+        unreachable!("{}", message);
     }
     Ok(())
 }

src/bin/ion/commands/beta/schema/mod.rs

@@ -35,7 +35,7 @@ pub fn run(_command_name: &str, matches: &ArgMatches<'static>) -> Result<()> {
             "The requested schema command ('{}') is not supported and clap did not generate an error message.",
             command_name
         );
-        unreachable!(message);
+        unreachable!("{}", message);
     }
     Ok(())
 }
@@ -46,4 +46,4 @@ pub fn app() -> CommandConfig {
             "The 'schema' command is a namespace for commands that are related to schema sandbox",
         )
         .subcommands(schema_subcommands())
-}
+}

src/bin/ion/main.rs

@@ -29,7 +29,7 @@ fn main() -> Result<()> {
             "The requested command ('{}') is not supported and clap did not generate an error message.",
             command_name
         );
-        unreachable!(message);
+        unreachable!("{}", message);
     }
     Ok(())
 }