Fix some rustdoc error capitalization

src/test/rustdoc-ui/doc-without-codeblock.rs

@@ -1,13 +1,13 @@
-#![deny(missing_doc_code_examples)] //~ ERROR Missing code example in this documentation
+#![deny(missing_doc_code_examples)] //~ ERROR missing code example in this documentation
 
 /// Some docs.
-//~^ ERROR Missing code example in this documentation
+//~^ ERROR missing code example in this documentation
 pub struct Foo;
 
 /// And then, the princess died.
-//~^ ERROR Missing code example in this documentation
+//~^ ERROR missing code example in this documentation
 pub mod foo {
     /// Or maybe not because she saved herself!
-    //~^ ERROR Missing code example in this documentation
+    //~^ ERROR missing code example in this documentation
     pub fn bar() {}
 }