Update __init__.py

opencv==4.5.1 builld faild with ndk-r25b 
opencv == 4.7.0 build done with ndk-r25b

Author: Sahil-pixel

pythonforandroid/recipes/opencv/__init__.py

@@ -15,7 +15,7 @@ class OpenCVRecipe(NDKRecipe):
         build of most of the libraries of the opencv's package, so we can
         process images, videos, objects, photos...
     '''
-    version = '4.5.1'
+    version = '4.7.0'
     url = 'https://github.com/opencv/opencv/archive/{version}.zip'
     depends = ['numpy']
     patches = ['patches/p4a_build.patch']