Bring back a method for 𝒩 (#63)

* Bring back a method for 𝒩

* Fix appveyor to test from Julia0.6 on

Author: lbenet

appveyor.yml

@@ -1,10 +1,14 @@
 environment:
   matrix:
-  - JULIA_URL: "https://julialang-s3.julialang.org/bin/winnt/x86/0.5/julia-0.5-latest-win32.exe"
-  - JULIA_URL: "https://julialang-s3.julialang.org/bin/winnt/x64/0.5/julia-0.5-latest-win64.exe"
+  - JULIA_URL: "https://julialang-s3.julialang.org/bin/winnt/x86/0.6/julia-0.6-latest-win32.exe"
+  - JULIA_URL: "https://julialang-s3.julialang.org/bin/winnt/x64/0.6/julia-0.6-latest-win64.exe"
+
+matrix:
+  allow_failures:
   - JULIA_URL: "https://julialangnightlies-s3.julialang.org/bin/winnt/x86/julia-latest-win32.exe"
   - JULIA_URL: "https://julialangnightlies-s3.julialang.org/bin/winnt/x64/julia-latest-win64.exe"
 
+
 branches:
   only:
     - master

src/contractors.jl

@@ -71,6 +71,11 @@ function 𝒩{T}(f, f′, X::Interval{T})
     m - (f(m) / f′(X))
 end
 
+function 𝒩{T}(f, X::Interval{T}, dX::Interval{T})
+    m = Interval(mid(X, where_bisect))
+
+    m - (f(m) / dX)
+end
 
 IntervalArithmetic.mid(X::IntervalBox, α) = mid.(X, α)