[C] Fix javadoc.

Author: denizevrenci

sbe-tool/src/main/java/uk/co/real_logic/sbe/util/ValidationUtil.java

@@ -43,7 +43,7 @@ public class ValidationUtil
  * must have all elements be a letter or digit or '_'. The first character must not be a digit.
  * And must not be a C keyword.
  * <p>
- * http://en.cppreference.com/w/cpp/keyword
+ * http://en.cppreference.com/w/c/keyword
  *
  * @param value to check
  * @return true for validity as a C name. false if not.