Spellchecking some comments

This PR attempts to clean up some minor spelling mistakes in comments

compiler/rustc_errors/src/styled_buffer.rs

@@ -26,7 +26,7 @@ impl StyledBuffer {
         StyledBuffer { lines: vec![] }
     }
 
-    /// Returns content of `StyledBuffer` splitted by lines and line styles
+    /// Returns content of `StyledBuffer` split by lines and line styles
     pub fn render(&self) -> Vec<Vec<StyledString>> {
         // Tabs are assumed to have been replaced by spaces in calling code.
         debug_assert!(self.lines.iter().all(|r| !r.iter().any(|sc| sc.chr == '\t')));