Pin opencv recipe revision number

The revision number immediately following presents a compilation error.
This commit pins the revision for now until more time is available to
debug a long term solution.

conanfile.py

@@ -186,7 +186,7 @@ def system_requirements(self):
     def requirements(self):
         if self.options.opNav:
             self.requires.add("pcre/8.45")
-            self.requires.add("opencv/4.1.2")
+            self.requires.add("opencv/4.1.2#b610ad323f67adc1b51e402cb5d68d70")
             self.options['opencv'].with_ffmpeg = False  # video frame encoding lib
             self.options['opencv'].with_ade = False  # graph manipulations framework
             self.options['opencv'].with_tiff = False  # generate image in TIFF format