The shebang in the python stub template was incorrectly patched to

<store-path>/bin/env python

instead of

<store-path>/bin/python

The reason was that patchShebangs was called with --replace which is
an unknown argument.

patching script interpreter paths in src/main/java/com/google/devtools/build/lib/bazel/rules/python/python_stub_template.txt --replace /usr/bin/env python /nix/store/w7gsq8v86hni4ynaqgwwlnlny115ylng-python3-3.7.4/bin/python
find: unknown predicate `--replace'

Using substituteInPlace instead resolves that issue.

Motivation for this change

The wrong shebang caused failures of py_binary targets due to python
not being in PATH in certain circumstances.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @Profpatsch