Update swift version to 5.4

[jonicong]

This also solve issue when installing with SPM on latest release.

Error log:

the manifest is missing a Swift tools version specification; consider prepending to the manifest '// swift-tools-version:5.4.0' to specify the current Swift toolchain version as the lowest Swift version supported by the project; if such a specification already exists, consider moving it to the top of the manifest, or prepending it with '//' to help Swift Package Manager find it

Info:

• Using Xcode 12.5