Revert use gzip for linux

Uses tar -a flag to determine compression algorithm based off file extension (so linux will continue to use xz and macOS can use gzip)

.travis-upload.sh

@@ -5,12 +5,14 @@ if [ "$TRAVIS_EVENT_TYPE" = "push" ]&&[ "$TRAVIS_BRANCH" = "master" ]; then
 
     if [ "$TRAVIS_OS_NAME" = "linux" -o -z "$TRAVIS_OS_NAME" ]; then
         REV_NAME="citra-linux-${GITDATE}-${GITREV}"
+        ARCHIVE_NAME="${REV_NAME}.tar.xz"
         mkdir "$REV_NAME"
 
         cp build/src/citra/citra "$REV_NAME"
         cp build/src/citra_qt/citra-qt "$REV_NAME"
     elif [ "$TRAVIS_OS_NAME" = "osx" ]; then
         REV_NAME="citra-osx-${GITDATE}-${GITREV}"
+        ARCHIVE_NAME="${REV_NAME}.tar.gz"
         mkdir "$REV_NAME"
 
         cp build/src/citra/Release/citra "$REV_NAME"
@@ -118,8 +120,7 @@ EOL
     cp license.txt "$REV_NAME"
     cp README.md "$REV_NAME"
 
-    ARCHIVE_NAME="${REV_NAME}.tar.gz"
-    tar -czvf "$ARCHIVE_NAME" "$REV_NAME"
+    tar -cavf "$ARCHIVE_NAME" "$REV_NAME"
 
     # move the compiled archive into the artifacts directory to be uploaded by travis releases
     mv "$ARCHIVE_NAME" artifacts/