py2: kpi: Add @staticmethod in between @func and __new__

Else on py2 it breaks as e.g.

    TypeError: unbound method __new__() must be called with Measurement instance as first argument (got type instance instead)

On py3 it works ok without explicit @staticmethod -> probably something
to fix on pygolang side.

kpi.py

@@ -223,6 +223,7 @@ class Interval(np.void):
 
 # Measurement() creates new Measurement instance with all data initialized to NA.
 @func(Measurement)
+@staticmethod
 def __new__(cls):
     m = _newscalar(cls, cls._dtype)
     for field in m._dtype0.names:
@@ -697,6 +698,7 @@ def _miter(calc): # -> iter(Measurement)
 
 # Interval(lo,hi) creates new interval with specified boundaries.
 @func(Interval)
+@staticmethod
 def __new__(cls, lo, hi):
     i = _newscalar(cls, cls._dtype)
     i['lo'] = lo