fix fastspar homebrew script

fastspar.rb

class Fastspar < Formula
  desc " Rapid and scalable correlation estimation for compositional data"
  homepage "https://github.com/scwatts/fastspar"
  url "https://github.com/scwatts/fastspar/archive/v0.0.5.tar.gz"
  sha256 "c4cc7682720f566da7587e555b58a688671a97235d00c33d042a7f2cd6cef20a"
  head "https://github.com/scwatts/fastspar.git"

  depends_on "armadillo" => :run
  depends_on "gsl" => :run
  depends_on "gnu-getopt" => :run
  depends_on "openblas" => :run

  needs :openmp

  def install
    system "./configure", "CC=gcc-7",
                          "CXX=g++-7",
                          "LDFLAGS=-L/usr/local/opt/openblas/lib",
                          "--prefix=#{prefix}"
    system "make", "-j", "install"
  end

  test do
    system "false"
  end
end