bugfix/communications (#8)

This PR contains the work done to add a missing public initialiser to the `MockURLRequest` struct of the `Communications` library. In addition, it also implements the `gmt` static property for the `TimeZone+Zone` extension included in the `Core` library.

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: #8

Sources/Core/Extensions/TimeZone+Zone.swift

@@ -0,0 +1,10 @@
+import Foundation
+
+public extension TimeZone {
+    
+    // MARK: Zones
+
+    /// Greenwich Mean Time or UTC+0
+    static let gmt = TimeZone(secondsFromGMT: 0)
+    
+}