fix: pylightning to_btc_str precision

The old codes if % 1000 statement logic was simply inverted
and produced the opposite output of the intention behin it.

Before Fix:
 - Millisatoshi('42sat').to_btc_str() => 0.00000042000btc
 - Millisatoshi('42001msat').to_btc_str() => 0.00000042btc

After  Fix:
 - Millisatoshi('42sat').to_btc_str() => 0.00000042btc
 - Millisatoshi('42001msat').to_btc_str() => 0.00000042001btc

contrib/pylightning/lightning/lightning.py

@@ -81,9 +81,9 @@ def to_btc_str(self):
         Return a string of form 12.34567890btc or 12.34567890123btc.
         """
         if self.millisatoshis % 1000:
-            return '{:.8f}btc'.format(self.to_btc())
-        else:
             return '{:.11f}btc'.format(self.to_btc())
+        else:
+            return '{:.8f}btc'.format(self.to_btc())
 
     def to_json(self):
         return self.__repr__()