Fix ExceptionInfo usage for pytest 4.1

Fix #384

changelog/384.bugfix.rst

@@ -0,0 +1 @@
+Add support for pytest 4.1.

xdist/workermanage.py

@@ -345,6 +345,10 @@ class WorkerController(object):
         except:  # noqa
             from _pytest._code import ExceptionInfo
 
+            # ExceptionInfo API changed in pytest 4.1
+            if hasattr(ExceptionInfo, "from_current"):
+                excinfo = ExceptionInfo.from_current()
+            else:
                 excinfo = ExceptionInfo()
             print("!" * 20, excinfo)
             self.config.notify_exception(excinfo)