fix(pptx): accommodate invalid image/jpg MIME-type

As described in #3381, some clients, perhaps including Adobe PDF
Converter, map JPEG images to the invalid `image/jpg` MIME-type. Prior
to v1.0.0, `python-pptx` would not load these images, which caused image
extraction to fail.

Update the `python-pptx` dependency to `v1.0.0` or above to ensure this
upstream fix is always available.

requirements/extra-pptx.in

@@ -1,3 +1,3 @@
 -c ./deps/constraints.txt
 
-python-pptx<=0.6.23
+python-pptx>=1.0.0