Changed Schannel string to SSL-Windows-native.

This is more descriptive for the user who might
not even know what schannnel is at all.
diff --git a/lib/curl_schannel.c b/lib/curl_schannel.c
index 0f49e8d..7dd227e 100644
--- a/lib/curl_schannel.c
+++ b/lib/curl_schannel.c
@@ -977,7 +977,7 @@
 
 size_t Curl_schannel_version(char *buffer, size_t size)
 {
-  size = snprintf(buffer, size, "schannel");
+  size = snprintf(buffer, size, "SSL-Windows-native");
 
   return size;
 }