Edited a typo

Author: superbspeed

doc/python/v4-migration.md

@@ -270,7 +270,7 @@ Prior to version 4, when plotly.py was passed a `datetime` that included a timez
 
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 ### Headless image export on Linux with Xvfb.
-In version 4, the static image export logic attempts to automatically detect whether to call the orca image export utility using Xvfb.  Xvfb is needed for orca to work in a Linux environment if an X11 display server is not available. By default, Xvfb us used if plotly.py is running on Linux if no X11 display server is detected and `Xvfb` is available on the system `PATH`.
+In version 4, the static image export logic attempts to automatically detect whether to call the orca image export utility using Xvfb.  Xvfb is needed for orca to work in a Linux environment if an X11 display server is not available. By default, Xvfb is used on Linux if no X11 display server is detected and `Xvfb` is available on the system `PATH`.
 
 This new behavior can be disabled by setting the `use_xvfb` orca configuration option to `False` as follows: