Disable Zint barcode backend for zint-2.7.x (#86)

- New zint API is incompatible, may eventually create a compatible backend

Author: j-evins

Diff for: CMakeLists.txt

@@ -126,7 +126,7 @@ endif ()
 find_package (ZLIB 1.2 QUIET)
 find_package (GnuBarcode 0.98 QUIET)
 find_package (LibQrencode 3.4 QUIET)
-find_package (LibZint 2.6 QUIET)
+find_package (LibZint 2.6 EXACT QUIET)
 # Unit testing support
 find_package (Qt5Test 5.4 QUIET)