fix typo

* NEWS, README.EXT: fix typo.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45632 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -110,5 +110,5 @@ with all sufficient information, see the ChangeLog file.
 
 * `rb_str_substr()` and `rb_str_subseq()` now share middle of a string,
   but not only the end of a string.  Therefore, result strings may not
-  be NULL-terminated, `StringValueCStr()` is needed calling to obtain a
-  NULL-terminated C string.
+  be NUL-terminated, `StringValueCStr()` is needed calling to obtain a
+  NUL-terminated C string.

README.EXT

@@ -1088,7 +1088,7 @@ RSTRING_LEN(str) ::
 RSTRING_PTR(str) ::
 
   String -> pointer to String data
-  Note that the result pointer may not be NULL-terminated
+  Note that the result pointer may not be NUL-terminated
 
 StringValue(value) ::
 
@@ -1100,8 +1100,8 @@ StringValuePtr(value) ::
 
 StringValueCStr(value) ::
 
-  Object with #to_str -> pointer to String data without NULL bytes
-  It is guaranteed that the result data is NULL-terminated
+  Object with #to_str -> pointer to String data without NUL bytes
+  It is guaranteed that the result data is NUL-terminated
 
 rb_str_new2(s) ::