rustdoc: Filter out another invalid id character

src/rustdoc/markdown_index_pass.rs

@@ -121,6 +121,7 @@ fn remove_punctuation(s: str) -> str {
         let s = str::replace(s, "/", "");
         let s = str::replace(s, ":", "");
         let s = str::replace(s, "&", "");
+        let s = str::replace(s, "^", "");
         ret s;
     }
     fn replace_with_hyphens(s: str) -> str {
@@ -139,6 +140,8 @@ fn should_remove_punctuation_from_headers() {
         == "impl-of-numnum-for-int";
     assert pandoc_header_id("impl of num::num for int/&")
         == "impl-of-numnum-for-int";
+    assert pandoc_header_id("impl of num::num for ^int")
+        == "impl-of-numnum-for-int";
 }
 
 #[test]