use cleaner working dir selection in check scripts

tools/check-localized-metadata.py

@@ -5,7 +5,7 @@ import os
 import re
 import sys
 
-os.chdir(os.path.dirname(__file__) + '/../')
+os.chdir(os.path.join(os.path.dirname(__file__), '..'))
 
 count = 0
 

tools/check-metadata-summary-whitespace.py

@@ -3,7 +3,7 @@
 import glob
 import os
 
-os.chdir(os.path.dirname(__file__) + '/../')
+os.chdir(os.path.join(os.path.dirname(__file__), '..'))
 
 for f in glob.glob('metadata/*/*/*.txt') +  glob.glob('metadata/*/*/*/*.txt'):
     if os.path.getsize(f) == 0: