MLECO-2235: Fix documentation

Signed-off-by: Isabella Gottardi <isabella.gottardi@arm.com>
Change-Id: If8d6bf60cd4961be4c29f46ea75422b093185b04
diff --git a/build_default.py b/build_default.py
index e4aa59d..b863c51 100755
--- a/build_default.py
+++ b/build_default.py
@@ -104,7 +104,7 @@
                         action="store_true")
     args = parser.parse_args()
 
-    logging.basicConfig(filename='log_build_default.log', level=logging.DEBUG)
+    logging.basicConfig(filename='log_build_default.log', level=logging.DEBUG, filemode='w')
     logging.getLogger().addHandler(logging.StreamHandler(sys.stdout))
 
     run(args.toolchain.lower(), not args.skip_download, not args.skip_vela)