Resolve semicolon_in_expressions_from_macros warning in serde_test

    warning: trailing semicolon in macro used in expression position
       --> serde_test/src/ser.rs:44:10
        |
    44  |         );
        |          ^
    ...
    152 |             Some(&Token::BorrowedStr(_)) => assert_next_token!(self, BorrowedStr(v)),
        |                                             ---------------------------------------- in this macro invocation
        |
        = note: `#[warn(semicolon_in_expressions_from_macros)]` on by default
        = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
        = note: this warning originates in the macro `assert_next_token` (in Nightly builds, run with -Z macro-backtrace for more info)

    warning: trailing semicolon in macro used in expression position
       --> serde_test/src/ser.rs:36:76
        |
    36  |         assert_next_token!($ser, stringify!($actual), Token::$actual, true);
        |                                                                            ^
    ...
    386 |             Token::TupleVariantEnd => assert_next_token!(self.ser, TupleVariantEnd),
        |                                       --------------------------------------------- in this macro invocation
        |
        = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
        = note: this warning originates in the macro `assert_next_token` (in Nightly builds, run with -Z macro-backtrace for more info)

serde_test/src/ser.rs

@@ -32,18 +32,18 @@ impl<'a> Serializer<'a> {
 }
 
 macro_rules! assert_next_token {
-    ($ser:expr, $actual:ident) => {
+    ($ser:expr, $actual:ident) => {{
         assert_next_token!($ser, stringify!($actual), Token::$actual, true);
-    };
-    ($ser:expr, $actual:ident($v:expr)) => {
+    }};
+    ($ser:expr, $actual:ident($v:expr)) => {{
         assert_next_token!(
             $ser,
             format_args!(concat!(stringify!($actual), "({:?})"), $v),
             Token::$actual(v),
             v == $v
         );
-    };
-    ($ser:expr, $actual:ident { $($k:ident),* }) => {
+    }};
+    ($ser:expr, $actual:ident { $($k:ident),* }) => {{
         let compare = ($($k,)*);
         let field_format = || {
             use std::fmt::Write;
@@ -59,7 +59,7 @@ macro_rules! assert_next_token {
             Token::$actual { $($k),* },
             ($($k,)*) == compare
         );
-    };
+    }};
     ($ser:expr, $actual:expr, $pat:pat, $guard:expr) => {
         match $ser.next_token() {
             Some($pat) if $guard => {}