Fix references to the license text

Update the references to the file "LICENCE" with "COPYING".

The file LICENCE doesn't exist in ruby/ruby nor ruby/openssl. This has
been always the case since OpenSSL for Ruby 2 was merged to the ruby
tree as a standard library in 2003.

In OpenSSL for Ruby 2's CVS repository[1], the LICENCE file contained
an old version of the Ruby License, identical to the COPYING file that
was in Ruby's tree at that time (r4128[2]).

[1] http://cvs.savannah.gnu.org/viewvc/rubypki/ossl2/LICENCE?revision=1.1.1.1&view=markup
[2] https://github.com/ruby/ruby/blob/231247c010acba191b78ed2d1310c935e63ad919/COPYING

Author: rhenium

ext/openssl/extconf.rb

@@ -8,7 +8,7 @@
 
 = Licence
   This program is licensed under the same licence as Ruby.
-  (See the file 'LICENCE'.)
+  (See the file 'COPYING'.)
 =end
 
 require "mkmf"

ext/openssl/openssl_missing.c

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 #include RUBY_EXTCONF_H
 

ext/openssl/openssl_missing.h

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 #if !defined(_OSSL_OPENSSL_MISSING_H_)
 #define _OSSL_OPENSSL_MISSING_H_

ext/openssl/ossl.c

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 #include "ossl.h"
 #include <stdarg.h> /* for ossl_raise */

ext/openssl/ossl.h

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 #if !defined(_OSSL_H_)
 #define _OSSL_H_

ext/openssl/ossl_asn1.c

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 #include "ossl.h"
 

ext/openssl/ossl_asn1.h

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 #if !defined(_OSSL_ASN1_H_)
 #define _OSSL_ASN1_H_

ext/openssl/ossl_bio.c

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 #include "ossl.h"
 

ext/openssl/ossl_bio.h

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 #if !defined(_OSSL_BIO_H_)
 #define _OSSL_BIO_H_

ext/openssl/ossl_bn.c

@@ -5,7 +5,7 @@
  */
 /*
  * This program is licensed under the same licence as Ruby.
- * (See the file 'LICENCE'.)
+ * (See the file 'COPYING'.)
  */
 /* modified by Michal Rokos <m.rokos@sh.cvut.cz> */
 #include "ossl.h"