Update text_detection.py

there is a recent change, how `std::vector<int>` is wrapped in python, 
it used to be a 2d array (requirig that weird `[0]` indexing), now it is only 1d

samples/dnn/text_detection.py

@@ -187,7 +187,7 @@ def main():
         indices = cv.dnn.NMSBoxesRotated(boxes, confidences, confThreshold, nmsThreshold)
         for i in indices:
             # get 4 corners of the rotated rect
-            vertices = cv.boxPoints(boxes[i[0]])
+            vertices = cv.boxPoints(boxes[i])
             # scale the bounding box coordinates based on the respective ratios
             for j in range(4):
                 vertices[j][0] *= rW