debian/copyright: Fix src/rt/miniz.c 'unlicense'

src/rt/miniz.c is public domain, but uses 'unlicense' wording.

Related lintian warning:
W: rust source: missing-license-paragraph-in-dep5-copyright public-domain (paragraph at line 21)

Signed-off-by: Jordan Justen <jljusten@gmail.com>

debian/copyright

@@ -16,7 +16,31 @@ License: Expat or Apache-2.0
 
 Files: src/rt/miniz.c
 Copyright: 1996 Rich Geldreich
-License: public-domain
+License: unlicense
+ This is free and unencumbered software released into the public domain.
+ .
+ Anyone is free to copy, modify, publish, use, compile, sell, or
+ distribute this software, either in source code form or as a compiled
+ binary, for any purpose, commercial or non-commercial, and by any
+ means.
+ .
+ In jurisdictions that recognize copyright laws, the author or authors
+ of this software dedicate any and all copyright interest in the
+ software to the public domain. We make this dedication for the
+ benefit of the public at large and to the detriment of our heirs and
+ successors. We intend this dedication to be an overt act of
+ relinquishment in perpetuity of all present and future rights to this
+ software under copyright law.
+ .
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
+ CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ .
+ For more information, please refer to <http://unlicense.org/>
 
 Files: src/rt/uthash/*
 Copyright: 2003-2009, Troy D. Hanson