easy.py change - fixes #42

The ValueError being thrown is because grid.py is not executable. This change fixes that issue.

This has been discussed prior:
shackenberg/Minimal-Bag-of-Visual-Words-Image-Classifier#2 [English]
http://www.cnblogs.com/zklidd/p/3990915.html [Chinese]

tools/easy.py

@@ -49,7 +49,7 @@
 print('Scaling training data...')
 Popen(cmd, shell = True, stdout = PIPE).communicate()	
 
-cmd = '{0} -svmtrain "{1}" -gnuplot "{2}" "{3}"'.format(grid_py, svmtrain_exe, gnuplot_exe, scaled_file)
+cmd = 'python {0} -svmtrain "{1}" -gnuplot "{2}" "{3}"'.format(grid_py, svmtrain_exe, gnuplot_exe, scaled_file)
 print('Cross validation...')
 f = Popen(cmd, shell = True, stdout = PIPE).stdout