nixos/make-options-doc: eat newlines in MD admonitions

leaving some newlines around after an admonition was closed causes the
newline rule to match, which in turn inserts literallayout newlines into
te xml output. that's not what we want.

nixos/lib/make-options-doc/mergeJSON.py

@@ -151,7 +151,7 @@ def p_manpage(md):
     md.inline.rules.append('manpage')
 
 def p_admonition(md):
-    ADMONITION_PATTERN = re.compile(r'^::: \{([^\n]*?)\}\n(.*?)^:::\n', flags=re.MULTILINE|re.DOTALL)
+    ADMONITION_PATTERN = re.compile(r'^::: \{([^\n]*?)\}\n(.*?)^:::$\n*', flags=re.MULTILINE|re.DOTALL)
     def parse(self, m, state):
         return {
             'type': 'admonition',