[Variable] Use Swift split over Foundation

Stencil/Variable.swift

@@ -6,7 +6,7 @@ class FilterExpression : Resolvable {
   let variable: Variable
 
   init(token: String, parser: TokenParser) throws {
-    let bits = token.componentsSeparatedByString("|")
+    let bits = token.characters.split("|").map(String.init)
     if bits.isEmpty {
       filters = []
       variable = Variable("")
@@ -43,7 +43,7 @@ public struct Variable : Equatable, Resolvable {
   }
 
   private func lookup() -> [String] {
-    return variable.componentsSeparatedByString(".")
+    return variable.characters.split(".").map(String.init)
   }
 
   /// Resolve the variable in the given context