Resolve "Learner1D fails when function returns a list instead of a numpy.array"

Closes #96 (closed)

adaptive/learner/learner1D.py

@@ -217,7 +217,7 @@ class Learner1D(BaseLearner):
         if real:
             # either it is a float/int, if not, try casting to a np.array
             if not isinstance(y, (float, int)):
-                y = np.asarray(y, dtype='float64')
+                y = np.asarray(y, dtype=float)
 
             # Add point to the real data dict
             self.data[x] = y