haskell-pandoc: disable 'doCheck' to avoid test suite build errors

Configuring pandoc-1.10.1...
Setup: At least the following dependencies are missing:
Diff ==0.2.*,
HUnit ==1.2.*,
QuickCheck >=2.4 && <2.6,
ansi-terminal >=0.5 && <0.7,
test-framework >=0.3 && <0.9,
test-framework-hunit >=0.2 && <0.4,
test-framework-quickcheck2 >=0.2.9 && <0.4