Fix title for admonitions

sphinx_gemini_builder/writer.py

@@ -128,7 +128,7 @@ class GeminiTranslator(SphinxTranslator):
 
     def depart_title(self, node: Element) -> None:
         if isinstance(node.parent, nodes.Admonition):
-            self.add_text(':')
+            self.add_text(': ')
 
     def visit_subtitle(self, node: Element) -> None:
         pass