remove call to Core.Inference to try to fix v0.7

Author: rdeits

src/b-splines/b-splines.jl

@@ -25,7 +25,7 @@ function BSplineInterpolation(::Type{TWeights}, A::AbstractArray{Tel,N}, ::IT, :
     for _ in 2:N
         c *= c
     end
-    T = Core.Inference.return_type(*, Tuple{typeof(c), Tel})
+    T = Base.promote_op(*, typeof(c), Tel)
 
     BSplineInterpolation{T,N,typeof(A),IT,GT,pad}(A)
 end