Title-case trait aliases section for consistency

Author: camelid

src/librustdoc/html/render/mod.rs

@@ -2527,7 +2527,7 @@ impl ItemSection {
             Self::OpaqueTypes => "Opaque Types",
             Self::AttributeMacros => "Attribute Macros",
             Self::DeriveMacros => "Derive Macros",
-            Self::TraitAliases => "Trait aliases",
+            Self::TraitAliases => "Trait Aliases",
         }
     }
 }

src/test/rustdoc/trait_alias.rs

@@ -8,7 +8,7 @@ use std::fmt::Debug;
 // @has foo/all.html '//a[@href="traitalias.Alias2.html"]' 'Alias2'
 // @has foo/all.html '//a[@href="traitalias.Foo.html"]' 'Foo'
 
-// @has foo/index.html '//h2[@id="trait-aliases"]' 'Trait aliases'
+// @has foo/index.html '//h2[@id="trait-aliases"]' 'Trait Aliases'
 // @has foo/index.html '//a[@class="traitalias"]' 'CopyAlias'
 // @has foo/index.html '//a[@class="traitalias"]' 'Alias2'
 // @has foo/index.html '//a[@class="traitalias"]' 'Foo'