Update Package.swift (#153)

Motivation
----------

I _believe_ the line `.package(path: "../.."),` in the `Package.swift`
of the Hummingbird example is vestigial from perhaps a previous version
where it was just a `Package.swift` and a `main.swift`. If it is need
explicitly for a container build, please mention in the docs because a
regular `swift build` to test the app locally doesn't work until it is
removed.

Modifications
-------------

removed the single line `.package(path: "../..")` from the
`Package.swift` in the Hummingbird example.

Result
------

Example will now build to be tested pre-containerization test. 

Test Plan
---------

Don't believe change needs a test as the example already does not have
tests.

---------

Co-authored-by: Euan Harris <euanh@apple.com>

Author: carlynorama

Examples/HelloWorldHummingbird/Package.swift

@@ -21,7 +21,7 @@ let package = Package(
     platforms: [.macOS(.v14)],
     dependencies: [
         .package(url: "https://github.com/hummingbird-project/hummingbird.git", from: "2.1.0"),
-        .package(path: "../.."),
+        .package(url: "https://github.com/apple/swift-container-plugin", from: "1.0.0"),
         .package(url: "https://github.com/apple/swift-argument-parser", from: "1.3.0"),
     ],
     targets: [