Update md_mermaid.py

fix long-known bug during dealing with unicode which has puzzled and effected some projects. You may find the detail in oruelle#2. Why I leave two `new_lines.append(line)`? Because in oruelle#2, @rayalan says his app depends on leading space, as a result I can't judge what we should do exactly. However, lets fix this to let most of the projects runs without problem again.

md_mermaid.py

@@ -16,9 +16,6 @@
 import re
 import string
 
-def strip_notprintable(myStr):
-    return ''.join(filter(lambda x: x in string.printable, myStr))
-
 MermaidRegex = re.compile(r"^(?P<mermaid_sign>[\~\`]){3}[\ \t]*[Mm]ermaid[\ \t]*$")
 
 
@@ -57,7 +54,7 @@ def run(self, lines):
                 new_lines.append("")
                 m_end = None
             elif in_mermaid_code:
-                new_lines.append(strip_notprintable(line).strip())
+                new_lines.append(line)
             else:
                 new_lines.append(line)