Add scikit-image

Previously it was required on OSX only.
Image tests now seem to require it.

Author: rocky

setup.py

@@ -78,9 +78,6 @@ def read(*rnames):
     CMDCLASS = {"build_ext": build_ext}
     INSTALL_REQUIRES += ["cython>=0.15.1"]
 
-if sys.platform == "darwin":
-    INSTALL_REQUIRES += ["scikit-image"]
-
 # General Requirements
 INSTALL_REQUIRES += [
     "sympy>=1.6, < 1.7",
@@ -92,6 +89,7 @@ def read(*rnames):
     "python-dateutil",
     "llvmlite",
     "requests",
+    "scikit-image",
     "wordcloud", # Used in builtin/image.py by WordCloud()
 ]