Reformat stack.yaml

[rcannon]

This fixes the stack build parsing error. However, there seems to be a GHC error when calling stack build:

ghc: panic! (the 'impossible' happened)
  (GHC version 8.2.2 for x86_64-apple-darwin):
	Prelude.chr: bad argument: 1543503875

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug


--  While building simple Setup.hs (scroll up to its section to see the error) using:
      /Users/cannon/.stack/programs/x86_64-osx/ghc-8.2.2/bin/ghc-8.2.2 -rtsopts -threaded -clear-package-db -global-package-db -hide-all-packages -package base -main-is StackSetupShim.mainOverride -package Cabal-2.0.1.0 /Users/cannon/.stack/setup-exe-src/setup-mPHDZzAJ.hs /Users/cannon/.stack/setup-exe-src/setup-shim-mPHDZzAJ.hs -o /Users/cannon/.stack/setup-exe-cache/x86_64-osx/tmp-Cabal-simple_mPHDZzAJ_2.0.1.0_ghc-8.2.2
    Process exited with code: ExitFailure 1

Note that my Mac has an Intel CPU.

[rcannon]

See Issue #20