opencv: build error on mac os x with mesonbuild

Not sure if the header should be modified, or if there's a proper compiler option to ignore this error.

When I use gst-build on Mac OSX, I got this error. Simply adding a space between >> solves this error.

In file included from ../subprojects/gst-plugins-bad/ext/opencv/gstopencv.cpp:45:
../subprojects/gst-plugins-bad/ext/opencv/gstcameracalibrate.h:96:38: error: a space is required between consecutive right angle brackets (use '> >')
  std::vector<std::vector<cv::Point2f>> imagePoints;
                                     ^~
                                     > >
1 error generated.