do not use `a' quoting style in comments

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/miscutils/adjtimex.c b/miscutils/adjtimex.c
index 04ba563..0830734 100644
--- a/miscutils/adjtimex.c
+++ b/miscutils/adjtimex.c
@@ -1,6 +1,6 @@
 /* vi: set sw=4 ts=4: */
 /*
- * adjtimex.c - read, and possibly modify, the Linux kernel `timex' variables.
+ * adjtimex.c - read, and possibly modify, the Linux kernel 'timex' variables.
  *
  * Originally written: October 1997
  * Last hack: March 2001