Use _snprintf for snprintf under Microsoft C in test/minigzip.c.
diff --git a/test/minigzip.c b/test/minigzip.c
index 0a1f81f..b3025a4 100644
--- a/test/minigzip.c
+++ b/test/minigzip.c
@@ -40,6 +40,10 @@
 #  define SET_BINARY_MODE(file)
 #endif
 
+#ifdef _MSC_VER
+#  define snprintf _snprintf
+#endif
+
 #ifdef VMS
 #  define unlink delete
 #  define GZ_SUFFIX "-gz"