Fix .travis.yml

Author: nemanjavlahovic

.travis.yml

@@ -37,5 +37,5 @@ script:
 # - xcodebuild test -project ./Shell\ Sort/Tests/Tests.xcodeproj -scheme Tests
 # - xcodebuild test -project ./Shortest\ Path\ \(Unweighted\)/Tests/Tests.xcodeproj -scheme Tests
 # - xcodebuild test -project ./Single-Source\ Shortest\ Paths\ \(Weighted\)/SSSP.xcodeproj -scheme SSSPTests
-# - xcodebuild test -project ./Stack/Tests/Tests.xcodeproj -scheme Tests
+  - xcodebuild test -project ./Stack/Tests/Tests.xcodeproj -scheme Tests
 # - xcodebuild test -project ./Topological\ Sort/Tests/Tests.xcodeproj -scheme Tests