point requirements.txt to custom arraycontext

Author: alexfikl

requirements.txt

@@ -4,7 +4,7 @@ git+https://github.com/inducer/pymbolic#egg=pymbolic
 git+https://github.com/inducer/islpy#egg=islpy
 git+https://github.com/inducer/loopy#egg=loopy
 git+https://github.com/inducer/pyfmmlib#egg=pyfmmlib
-git+https://github.com/inducer/arraycontext#egg=arraycontext
+git+https://github.com/alexfikl/arraycontext@dataclass-annotations#egg=arraycontext
 
 # only for reference values for the fmmlib test
 # (unable to use---circular dep)