Fixed bug with .json path regular expression

I had a table called "geojson" and it caused an exception because the regex
was matching .json and not \.json

datasette/app.py

@@ -998,7 +998,7 @@ class Datasette:
         self.jinja_env.filters['quote_plus'] = lambda u: urllib.parse.quote_plus(u)
         self.jinja_env.filters['escape_table_name'] = escape_sqlite_table_name
         self.jinja_env.filters['to_css_class'] = to_css_class
-        app.add_route(IndexView.as_view(self), '/<as_json:(.jsono?)?$>')
+        app.add_route(IndexView.as_view(self), '/<as_json:(\.jsono?)?$>')
         # TODO: /favicon.ico and /-/static/ deserve far-future cache expires
         app.add_route(favicon, '/favicon.ico')
         app.static('/-/static/', str(app_root / 'datasette' / 'static'))
@@ -1006,7 +1006,7 @@ class Datasette:
             app.static(path, dirname)
         app.add_route(
             DatabaseView.as_view(self),
-            '/<db_name:[^/\.]+?><as_json:(.jsono?)?$>'
+            '/<db_name:[^/\.]+?><as_json:(\.jsono?)?$>'
         )
         app.add_route(
             DatabaseDownload.as_view(self),
@@ -1014,10 +1014,10 @@ class Datasette:
         )
         app.add_route(
             TableView.as_view(self),
-            '/<db_name:[^/]+>/<table:[^/]+?><as_json:(.jsono?)?$>'
+            '/<db_name:[^/]+>/<table:[^/]+?><as_json:(\.jsono?)?$>'
         )
         app.add_route(
             RowView.as_view(self),
-            '/<db_name:[^/]+>/<table:[^/]+?>/<pk_path:[^/]+?><as_json:(.jsono?)?$>'
+            '/<db_name:[^/]+>/<table:[^/]+?>/<pk_path:[^/]+?><as_json:(\.jsono?)?$>'
         )
         return app