Use "Setup Swift" action to install swift, and bump swift version to 5.4 (#129)

* Update SwiftPlot_Ubuntu.yml

* Update SwiftPlot_Ubuntu.yml

Author: KarthikRIyer

.github/workflows/SwiftPlot_Ubuntu.yml

@@ -5,9 +5,6 @@ on:
     branches: master
   pull_request:
 
-env:
-  SWIFT_VERSION: 5.2.1
-
 jobs:
   build:
 
@@ -19,12 +16,10 @@ jobs:
       run: sudo apt-get install libfreetype6-dev
     - name: Install Swift Dependencies
       run: sudo apt-get install clang libicu-dev
-    - name: Download Swift
-      run: wget "https://swift.org/builds/swift-${{ env.SWIFT_VERSION }}-release/ubuntu1804/swift-${{ env.SWIFT_VERSION }}-RELEASE/swift-${{ env.SWIFT_VERSION }}-RELEASE-ubuntu18.04.tar.gz"
     - name: Install Swift
-      run: |
-        tar xzf swift-${{ env.SWIFT_VERSION }}-RELEASE-ubuntu18.04.tar.gz
-        echo "::add-path::$(pwd)/swift-${{ env.SWIFT_VERSION }}-RELEASE-ubuntu18.04/usr/bin"
+      uses: fwal/setup-swift@v1
+      with:
+        swift-version: "5.4"
     - name: Build
       run: swift build -v
     - name: Run tests