Move node-semver to submodule and upgrade

- Despite the name, this is a python package
- The whole git module was vendored, so making it a submodule will make
  it easier to upgrade in the future
- Upgrade to the latest version to remove python3 syntax warnings from
  app staging logs

Author: Gerg

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "fixtures/composer_no_index_dot_php/vendor/psr/log"]
 	path = fixtures/composer_no_index_dot_php/vendor/psr/log
 	url = https://github.com/php-fig/log
+[submodule "python-vendor/node-semver"]
+	path = python-vendor/node-semver
+	url = [email protected]:podhmo/python-node-semver.git

extensions/composer/extension.py

@@ -31,7 +31,7 @@
 from extension_helpers import ExtensionHelper
 
 sys.path.append(os.path.join(os.path.dirname(os.path.abspath(__file__)), '..', '..', 'python-vendor', 'node-semver'))
-from semver import max_satisfying
+from nodesemver import max_satisfying
 
 from build_pack_utils.compile_extensions import CompileExtensions