[CI] Changed triton-nightly to --pre triton (#78)

The solution proposed in #77 can create namespace conflicts when triton and triton-nightly have both been pip installed. Therefore, this PR is moving nightly releases to pre-releases in the main triton index.

python/setup.py

@@ -97,10 +97,7 @@ setup(
     long_description="",
     packages=["triton", "triton/_C", "triton/ops", "triton/ops/blocksparse"],
     install_requires=["numpy", "torch"],
-    package_data={
-        "triton/ops": ["*.c"],
-        "triton/ops/blocksparse": ["*.c"]
-    },
+    package_data={"triton/ops": ["*.c"], "triton/ops/blocksparse": ["*.c"]},
     include_package_data=True,
     ext_modules=[CMakeExtension("triton", "triton/_C/")],
     cmdclass={"build_ext": CMakeBuild},