Update SnapshotTesting dependency

Using https://github.com/thedavidharris/swift-snapshot-testing.git, .revision(64c1925) for now, as the current release of SnapshotTesting does not compile.

See this issue for more details: pointfreeco/swift-snapshot-testing#350

 We are waiting for this PR to be merged, then we can revert this change: pointfreeco/swift-snapshot-testing#355

Author: zweigraf

Package.swift

@@ -16,7 +16,7 @@ let package = Package(
         .library(name: "TestingExtensionsDynamic", type: .dynamic, targets: ["TestingExtensions"])
     ],
     dependencies: [
-        .package(name: "SnapshotTesting", url: "https://github.com/pointfreeco/swift-snapshot-testing.git", .branch("master")),
+        .package(name: "SnapshotTesting", url: "https://github.com/thedavidharris/swift-snapshot-testing.git", .revision("64c1925")),
         .package(name: "SwiftRex", url: "https://github.com/SwiftRex/SwiftRex.git", from: "0.7.1")
     ],
     targets: [