Edit spelling mistake in my previous pull request

apps/traincascade/traincascade.cpp

@@ -6,7 +6,7 @@ using namespace cv;
 
 /*
 traincascade.cpp is the source file of the program used for cascade training.
-User has to provide training input in form of posotive and negative training images,
+User has to provide training input in form of positive and negative training images,
 and other data related to training in form of command line argument.
 */
 int main( int argc, char* argv[] )