test/py: use " for docstrings

Python's coding style docs indicate to use " not ' for docstrings.

test/py has other violations of the coding style docs, since the docs
specify a stranger style than I would expect, but nobody has complained
about those yet:-)

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

test/py/tests/test_000_version.py

@@ -9,7 +9,7 @@
 # command prompt.
 
 def test_version(u_boot_console):
-    '''Test that the "version" command prints the U-Boot version.'''
+    """Test that the "version" command prints the U-Boot version."""
 
     # "version" prints the U-Boot sign-on message. This is usually considered
     # an error, so that any unexpected reboot causes an error. Here, this