Fixes file header in src/{cdump,dump}.c [ci skip]

The file headers were pointing to each other's files.

src/cdump.c

 /*
-** dump.c - mruby binary dumper (mrbc binary format)
+** cdump.c - mruby binary dumper (in C)
 **
 ** See Copyright Notice in mruby.h
 */

src/dump.c

 /*
-** cdump.c - mruby binary dumper (in C)
+** dump.c - mruby binary dumper (mrbc binary format)
 **
 ** See Copyright Notice in mruby.h
 */