Update README.rst

Co-Authored-By: Andrew Murray <3112309+radarhere@users.noreply.github.com>

README.rst

@@ -96,7 +96,7 @@ The environment variable specified which Manylinux docker container you are buil
 The ``PLAT`` environment variable can be one of ``x86_64``, ``i686`` ``s390x``,
 ``ppc64le``, or ``aarch64``, specifying 64-bit x86, 32-bit x86, 64-bit s390x,
 PowerPC, and ARM builds, respectively.  The default is ``x86_64``. Only ``x86_64``
-and ``i686`` are valild on manylinux1 and manylinux2010.
+and ``i686`` are valid on manylinux1 and manylinux2010.
 
 ``multibuild/travis_linux_steps.sh`` defines the ``build_wheel`` function,
 which starts up the Manylinux1 Docker container to run a wrapper script