Add cabal constraint: process < 1.3

The gbc-tests dependencies require process < 1.3 leading to dependency
conflicts if the sandbox has been first populated with dependencies of
Bond library before configuring the test suite.

This is a (hopefully) temporary workaround until
pcapriotti/optparse-applicative#150 is merged.

compiler/bond.cabal

@@ -42,6 +42,7 @@ library
                     ghc-prim,
                     mtl >= 2.1,
                     parsec >= 3.1,
+                    process < 1.3,
                     shakespeare >= 2.0,
                     text >= 0.11
   ghc-options:      -Wall