Fix "an" usage

Author: arqunis

.travis.yml

@@ -194,7 +194,7 @@ after_failure:
 
 # Save tagged docker images we created and load them if they're available
 # Travis saves caches whether the build failed or not, nuke rustsrc if
-# the failure was while updating it (as it may be in an bad state)
+# the failure was while updating it (as it may be in a bad state)
 # https://github.com/travis-ci/travis-ci/issues/4472
 before_cache:
   - docker history -q rust-ci |

src/libsyntax/parse/parser.rs

@@ -2707,7 +2707,7 @@ impl<'a> Parser<'a> {
                 let (span, e) = self.interpolated_or_expr_span(e)?;
                 let span_of_tilde = lo;
                 let mut err = self.diagnostic().struct_span_err(span_of_tilde,
-                        "`~` can not be used as an unary operator");
+                        "`~` can not be used as a unary operator");
                 err.span_label(span_of_tilde, &"did you mean `!`?");
                 err.help("use `!` instead of `~` if you meant to perform bitwise negation");
                 err.emit();