change template context key: version_string -> inventory_version_string

So it's more unique ;)

inventory/context_processors.py

@@ -2,4 +2,4 @@ from inventory import __version__
 
 
 def inventory_version_string(request):
-    return {"version_string": f"v{__version__}"}
+    return {'inventory_version_string': f'v{__version__}'}

inventory_project/templates/admin/base_site.html

@@ -7,11 +7,11 @@
     <link rel="stylesheet" type="text/css" href="{% static 'inventory.css' %}">
 {% endblock %}
 
-{% block title %}{{ title }} | PyInventory {{ version_string }}{% endblock %}
+{% block title %}{{ title }} | PyInventory {{ inventory_version_string }}{% endblock %}
 
 {% block branding %}
 <h1 id="site-name">
-    <a href="{% url 'admin:index' %}">PyInventory {{ version_string }}</a>
+    <a href="{% url 'admin:index' %}">PyInventory {{ inventory_version_string }}</a>
 </h1>
 {% endblock %}