Add back in equalToSuperview API

Source/ConstraintMakerRelatable.swift

@@ -74,6 +74,14 @@ public class ConstraintMakerRelatable {
         return self.relatedTo(other, relation: .equal, file: file, line: line)
     }
     
+    @discardableResult
+    public func equalToSuperview(_ file: String = #file, _ line: UInt = #line) -> ConstraintMakerEditable {
+        guard let other = self.description.view.superview else {
+            fatalError("Expected superview but found nil when attempting make constraint `equalToSuperview`.")
+        }
+        return self.relatedTo(other, relation: .equal, file: file, line: line)
+    }
+    
     @discardableResult
     public func lessThanOrEqualTo(_ other: ConstraintRelatableTarget, _ file: String = #file, _ line: UInt = #line) -> ConstraintMakerEditable {
         return self.relatedTo(other, relation: .lessThanOrEqual, file: file, line: line)