Replace pystache package with chevron

This replaces the pystache package with the chevron package for rendering
mustache templates.

setup.py

@@ -87,7 +87,7 @@ def get_version(version_file):
     package_data={"lineage": ["templates/*.md"]},
     py_modules=[splitext(basename(path))[0] for path in glob("src/*.py")],
     include_package_data=True,
-    install_requires=["PyGithub", "pystache", "PyYAML", "setuptools >= 24.2.0"],
+    install_requires=["chevron", "PyGithub", "PyYAML", "setuptools >= 24.2.0"],
     extras_require={
         "test": [
             "coverage",

src/lineage/entrypoint.py

@@ -11,9 +11,9 @@
 from urllib.parse import ParseResult, urlparse
 
 # Third-Party Libraries
+import chevron
 from github import Github, PullRequest, Repository
 import pkg_resources
-import pystache
 import requests
 import yaml
 
@@ -372,13 +372,13 @@ def main() -> None:
                     }
                     if conflict_file_list:
                         title = f"⚠️ CONFLICT! Lineage pull request for: {lineage_id}"
-                        body = pystache.render(conflict_template, template_data)
+                        body = chevron.render(conflict_template, template_data)
                         create_pull_request(
                             repo, pr_branch_name, local_branch, title, body, draft=True
                         )
                     else:
                         title = f"Lineage pull request for: {lineage_id}"
-                        body = pystache.render(clean_template, template_data)
+                        body = chevron.render(clean_template, template_data)
                         create_pull_request(
                             repo, pr_branch_name, local_branch, title, body, draft=False
                         )