Fixed cheatsheet for loop (bug #2701)

doc/opencv_cheatsheet.tex

@@ -215,7 +215,7 @@
 \> \texttt{for(int y = 1; y < image.rows-1; y++) \{}\\
 \> \> \texttt{Vec3b* prevRow = image.ptr<Vec3b>(y-1);}\\
 \> \> \texttt{Vec3b* nextRow = image.ptr<Vec3b>(y+1);}\\
-\> \> \texttt{for(int x = 0; y < image.cols; x++)}\\
+\> \> \texttt{for(int x = 0; x < image.cols; x++)}\\
 \> \> \> \texttt{for(int c = 0; c < 3; c++)}\\
 \> \> \> \texttt{  dyImage.at<Vec3b>(y,x)[c] =}\\
 \> \> \> \texttt{    saturate\_cast<uchar>(}\\