Use resolver=2 in the workspace

It separates feature selection for different dependency classes (dev,
build, regular), which makes sense even if it seems to have no impact at
the moment.

Author: bluss

Cargo.toml

@@ -20,6 +20,7 @@ keywords = ["array", "data-structure", "multidimensional", "matrix", "blas"]
 categories = ["data-structures", "science"]
 
 exclude = ["docgen/images/*"]
+resolver = "2"
 
 [lib]
 name = "ndarray"