lib/color: Fix compilation with uClibc

elfutils passed -Werror and this call errors on uClibc with a mismatching
pointer type. Cast to char * to fix.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
diff --git a/lib/ChangeLog b/lib/ChangeLog
index 0914b2c..7381860 100644
--- a/lib/ChangeLog
+++ b/lib/ChangeLog
@@ -1,3 +1,7 @@
+2019-05-03  Rosen Penev  <rosenp@gmail.com>
+
+	* color.c (parse_opt): Cast program_invocation_short_name to char *.
+
 2018-11-04  Mark Wielaard  <mark@klomp.org>
 
 	* bpf.h: Add BPF_JLT, BPF_JLE, BPF_JSLT and BPF_JSLE.
diff --git a/lib/color.c b/lib/color.c
index 9ffbf55..20b9698 100644
--- a/lib/color.c
+++ b/lib/color.c
@@ -132,7 +132,7 @@
   - 'auto', 'tty', 'if-tty'\n"),
 		     program_invocation_short_name, arg);
 	      argp_help (&color_argp, stderr, ARGP_HELP_SEE,
-			 program_invocation_short_name);
+			 (char *) program_invocation_short_name);
 	      exit (EXIT_FAILURE);
 	    }
 	}