Fix typo, reported by Patrick Spendrin.
diff --git a/lib/zipint.h b/lib/zipint.h
index 6f13361..7b7220c 100644
--- a/lib/zipint.h
+++ b/lib/zipint.h
@@ -82,7 +82,7 @@
 #endif
 #if defined(HAVE__STRDUP)
 #if !defined(HAVE_STRDUP) || defined(_WIN32)
-#undefine strdup
+#undef strdup
 #define strdup		_strdup
 #endif
 #endif