update libsonic to v0.5.1

makes plugin work again on Kodi Krypton (fixes issue
https://github.com/basilfx/plugin.audio.subsonic/issues/3)

lib/libsonic/__init__.py

@@ -29,4 +29,4 @@ print conn.ping()
 
 from connection import *
 
-__version__ = '0.3.4'
+__version__ = '0.5.1'

lib/libsonic/errors.py

@@ -56,4 +56,4 @@ def getExcByCode(code):
     code = int(code)
     if code in ERR_CODE_MAP:
         return ERR_CODE_MAP[code]
-    return SonicError
+    return SonicError