Fix typo

Author: cactorium

src/librustc/diagnostics.rs

@@ -311,7 +311,7 @@ variable. This error can occur for several cases, the most common of which is
 that there is a mismatch in the expected type that the compiler inferred, and
 the actual type that the user defined a variable as.
 
-let a: char = 7;    // An integral type can't contained in a character, so 
+let a: char = 7;    // An integral type can't be contained in a character, so 
                     // there is a mismatch.
 
 let b: u32 = 7;     // Either use the right type...