Fix invalid markdown codeblock label

Author: GuillaumeGomez

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -88,7 +88,7 @@
 //!
 //! When generating the `expr` for the `A` impl, the `SubstructureFields` is
 //!
-//! ```{.text}
+//! ```text
 //! Struct(vec![FieldInfo {
 //!            span: <span of x>
 //!            name: Some(<ident of x>),
@@ -99,7 +99,7 @@
 //!
 //! For the `B` impl, called with `B(a)` and `B(b)`,
 //!
-//! ```{.text}
+//! ```text
 //! Struct(vec![FieldInfo {
 //!           span: <span of `i32`>,
 //!           name: None,
@@ -113,7 +113,7 @@
 //! When generating the `expr` for a call with `self == C0(a)` and `other
 //! == C0(b)`, the SubstructureFields is
 //!
-//! ```{.text}
+//! ```text
 //! EnumMatching(0, <ast::Variant for C0>,
 //!              vec![FieldInfo {
 //!                 span: <span of i32>
@@ -125,7 +125,7 @@
 //!
 //! For `C1 {x}` and `C1 {x}`,
 //!
-//! ```{.text}
+//! ```text
 //! EnumMatching(1, <ast::Variant for C1>,
 //!              vec![FieldInfo {
 //!                 span: <span of x>
@@ -137,7 +137,7 @@
 //!
 //! For the tags,
 //!
-//! ```{.text}
+//! ```text
 //! EnumTag(
 //!     &[<ident of self tag>, <ident of other tag>], <expr to combine with>)
 //! ```
@@ -149,7 +149,7 @@
 //!
 //! A static method on the types above would result in,
 //!
-//! ```{.text}
+//! ```text
 //! StaticStruct(<ast::VariantData of A>, Named(vec![(<ident of x>, <span of x>)]))
 //!
 //! StaticStruct(<ast::VariantData of B>, Unnamed(vec![<span of x>]))