Fixes docs for ASCII functions to no longer claim U+0021 is '@'.

Author: Nathan Ringo

src/libcore/num/mod.rs

@@ -2892,7 +2892,7 @@ impl u8 {
     }
 
     /// Checks if the value is an ASCII graphic character:
-    /// U+0021 '@' ... U+007E '~'.
+    /// U+0021 '!' ... U+007E '~'.
     ///
     /// # Examples
     ///

src/libstd/ascii.rs

@@ -245,7 +245,7 @@ pub trait AsciiExt {
     fn is_ascii_punctuation(&self) -> bool { unimplemented!(); }
 
     /// Checks if the value is an ASCII graphic character:
-    /// U+0021 '@' ... U+007E '~'.
+    /// U+0021 '!' ... U+007E '~'.
     /// For strings, true if all characters in the string are
     /// ASCII graphic characters.
     ///

src/libstd_unicode/char.rs

@@ -1332,7 +1332,7 @@ impl char {
     }
 
     /// Checks if the value is an ASCII graphic character:
-    /// U+0021 '@' ... U+007E '~'.
+    /// U+0021 '!' ... U+007E '~'.
     ///
     /// # Examples
     ///