Use the latest 5.3 snapshot in .swift-version

These SwiftWasm snapshots should be more stable in general and also have a workaround for swiftwasm/JavaScriptKit#6 included. They still use the old metadata layout, so Runtime and OpenCombine dependencies had to be updated in `Package.swift` for `@ObservableObject` to work with these snapshots.

Author: MaxDesiatov

.swift-version

@@ -1 +1 @@
-wasm-DEVELOPMENT-SNAPSHOT-2020-06-12-a
+wasm-5.3-SNAPSHOT-2020-07-27-a

Package.resolved

@@ -38,8 +38,8 @@ let package = Package(
     // Dependencies declare other packages that this package depends on.
     // .package(url: /* package url */, from: "1.0.0"),
     .package(url: "https://github.com/kateinoigakukun/JavaScriptKit.git", .revision("c90e82f")),
-    .package(url: "https://github.com/MaxDesiatov/Runtime.git", .branch("wasi-build")),
-    .package(url: "https://github.com/MaxDesiatov/OpenCombine.git", .branch("observable-object")),
+    .package(url: "https://github.com/MaxDesiatov/Runtime.git", .branch("wasi-build-5.3")),
+    .package(url: "https://github.com/MaxDesiatov/OpenCombine.git", .branch("observable-object-5.3")),
   ],
   targets: [
     // Targets are the basic building blocks of a package. A target can define