Duplicate instance declarations

[madjestic]

$ cabal install
...
[28 of 30] Compiling B1.Program.Chart.GraphUtilsTest ( tests/B1/Program/Chart/GraphUtilsTest.hs, dist/dist-sandbox-d2346a33/build/b1-tests/b1-tests-tmp/B1/Program/Chart/GraphUtilsTest.o )

tests/B1/Program/Chart/GraphUtilsTest.hs:39:10: error:
    Duplicate instance declarations:
      instance Arbitrary GLfloat
        -- Defined at tests/B1/Program/Chart/GraphUtilsTest.hs:39:10
      instance [safe] Arbitrary Float
        -- Defined in ‘Test.QuickCheck.Arbitrary’
cabal: Leaving directory '.'
cabal: Error: some packages failed to install:
b1-0.1 failed during the building phase. The exception was:
ExitFailure 1

$ ghc -V
> The Glorious Glasgow Haskell Compilation System, version 8.0.2
$ cabal -V
> cabal-install version 1.24.0.2
> compiled using version 1.24.2.0 of the Cabal library