Update copyright year.

lib/base64.c

@@ -1,5 +1,5 @@
 /* base64.c -- Encode binary data using printable characters.
-   Copyright (C) 1999-2001, 2004-2006, 2009-2017 Free Software Foundation, Inc.
+   Copyright (C) 1999-2001, 2004-2006, 2009-2018 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -12,13 +12,13 @@
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License
-   along with this program; if not, see <http://www.gnu.org/licenses/>.  */
+   along with this program; if not, see <https://www.gnu.org/licenses/>.  */
 
 /* Written by Simon Josefsson.  Partially adapted from GNU MailUtils
  * (mailbox/filter_trans.c, as of 2004-11-28).  Improved by review
  * from Paul Eggert, Bruno Haible, and Stepan Kasal.
  *
- * See also RFC 4648 <http://www.ietf.org/rfc/rfc4648.txt>.
+ * See also RFC 4648 <https://www.ietf.org/rfc/rfc4648.txt>.
  *
  * Be careful with error checking.  Here is how you would typically
  * use these functions:
@@ -345,7 +345,7 @@ base64_decode_ctx_init (struct base64_decode_context *ctx)
    and return CTX->buf.  In either case, advance *IN to point to the byte
    after the last one processed, and set *N_NON_NEWLINE to the number of
    verified non-newline bytes accessible through the returned pointer.  */
-static const char *
+static char *
 get_4 (struct base64_decode_context *ctx,
        char const *restrict *in, char const *restrict in_end,
        size_t *n_non_newline)
@@ -361,7 +361,7 @@ get_4 (struct base64_decode_context *ctx,
           /* This is the common case: no newline.  */
           *in += 4;
           *n_non_newline = 4;
-          return (const char *) t;
+          return (char *) t;
         }
     }