Update ffi/openssl.rb to load openssl 1.0 if available

This updates the `ffi_lib` call to specify some alternative libraries which will
prioritize loading openssl 1.0. This fixes an issue on hosts which have openssl
1.1 and 1.0 and would encounter an error for the `SSL_library_init` function not
being found.

Fixes lian#205

lib/bitcoin/ffi/openssl.rb

@@ -11,7 +11,7 @@ module OpenSSL_EC
   if FFI::Platform.windows?
     ffi_lib 'libeay32', 'ssleay32'
   else
-    ffi_lib 'ssl'
+    ffi_lib [ 'libssl.so.1.0.0', 'ssl' ]
   end
 
   NID_secp256k1 = 714