Update 'Core' test target name to 'CorePromise'

More descriptive name avoids target conflicts during swift build process
when depending on multiple packages that also have a 'Core' target

- Fixes Test: LinuxMain import of Core

Package.swift

@@ -26,5 +26,5 @@ pkg.swiftLanguageVersions = [3, 4]
 pkg.targets = [
     pmk,
     .testTarget(name: "A+", dependencies: ["PromiseKit"]),
-    .testTarget(name: "Core", dependencies: ["PromiseKit"], path: "Tests/CorePromise"),
+    .testTarget(name: "CorePromise", dependencies: ["PromiseKit"], path: "Tests/CorePromise"),
 ]

Tests/LinuxMain.swift

@@ -2,7 +2,7 @@
 // DO NOT EDIT
 
 
-@testable import Core
+@testable import CorePromise
 @testable import A_
 import XCTest