s/enum struct/enum class/

Both are semantically equivalent, and it appears that "enum struct" is
a little bit more confusing.

emper/strategies/AbstractWorkStealingScheduler.hpp

@@ -36,7 +36,7 @@ class AbstractWorkStealingScheduler : public Scheduler {
  public:
 	static const int QUEUE_SIZE = 1024;
 
-	enum struct FiberSource : uintptr_t {
+	enum class FiberSource : uintptr_t {
 		local,
 		stolen,
 		anywhere_queue,

emper/strategies/laws/LawsStrategy.hpp

@@ -18,7 +18,7 @@ class RuntimeStrategyStats;
 
 class LawsStrategy : public AbstractWorkStealingStrategy {
  private:
-	enum struct FiberSource : uintptr_t {
+	enum class FiberSource : uintptr_t {
 		local = static_cast<uintptr_t>(AbstractWorkStealingScheduler::FiberSource::local),
 		stolen = static_cast<uintptr_t>(AbstractWorkStealingScheduler::FiberSource::stolen),
 		anywhere_queue =