Don't check form of version number

This changes the regex in test_it_executes_git_not_from_cwd so
that (unlike test_it_executes_git_to_shell_and_returns_result) it
only checks that the output starts with the words "git version",
and not the form of whatever follows those words.

test/test_git.py

@@ -103,7 +103,7 @@ def test_it_executes_git_not_from_cwd(self):
                 os.chmod(impostor_path, 0o755)
 
             with _chdir(tmpdir):
-                self.assertRegex(self.git.execute(["git", "version"]), r"^git version [\d\.]{2}.*$")
+                self.assertRegex(self.git.execute(["git", "version"]), r"^git version\b")
 
     def test_it_accepts_stdin(self):
         filename = fixture_path("cat_file_blob")