fix: fix invalid rustdoc code block attributes

Author: xu-cheng

src/lib.rs

@@ -41,7 +41,7 @@ As a consequence, when calling another parsing function, either:
 
 Examples:
 
-```{rust,ignore}
+```rust,ignore
 // 'none' | <image>
 fn parse_background_image(context: &ParserContext, input: &mut Parser)
                                     -> Result<Option<Image>, ()> {
@@ -53,7 +53,7 @@ fn parse_background_image(context: &ParserContext, input: &mut Parser)
 }
 ```
 
-```{rust,ignore}
+```rust,ignore
 // [ <length> | <percentage> ] [ <length> | <percentage> ]?
 fn parse_border_spacing(_context: &ParserContext, input: &mut Parser)
                           -> Result<(LengthOrPercentage, LengthOrPercentage), ()> {

src/parser.rs

@@ -295,7 +295,7 @@ impl BlockType {
 ///
 /// The union of two sets can be obtained with the `|` operator. Example:
 ///
-/// ```{rust,ignore}
+/// ```rust,ignore
 /// input.parse_until_before(Delimiter::CurlyBracketBlock | Delimiter::Semicolon)
 /// ```
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]

src/serializer.rs

@@ -286,7 +286,7 @@ where
 ///
 /// Typical usage:
 ///
-/// ```{rust,ignore}
+/// ```rust,ignore
 /// fn write_foo<W>(foo: &Foo, dest: &mut W) -> fmt::Result where W: fmt::Write {
 ///     dest.write_str("\"")?;
 ///     {