Update for newer pytest (#44)

* Apply my suggestions from #43.

nbsmoke/__init__.py

@@ -140,7 +140,10 @@ def __init__(self, fspath, parent=None, config=None, session=None, dowhat=RunNb)
         super(IPyNbFile,self).__init__(fspath, parent=parent, config=None, session=None)
 
     def collect(self):
-        yield self._dowhat(str(self.fspath), self)
+        if hasattr(self._dowhat, "from_parent"):
+            yield self._dowhat.from_parent(self,name=str(self.fspath))
+        else: # older pytest (https://docs.pytest.org/en/stable/deprecations.html#node-construction-changed-to-node-from-parent)
+            yield self._dowhat(str(self.fspath), self)
 
 
 def pytest_collect_file(path, parent):
@@ -162,4 +165,7 @@ def pytest_collect_file(path, parent):
                 dowhat = LintNb
             elif opt.nbsmoke_verify:
                 dowhat = VerifyNb
-            return IPyNbFile(path, parent, dowhat=dowhat)
+            if hasattr(IPyNbFile, "from_parent"):
+                return IPyNbFile.from_parent(parent, fspath=path, dowhat=dowhat)
+            else: # for older pytest (https://docs.pytest.org/en/stable/deprecations.html#node-construction-changed-to-node-from-parent)
+                return IPyNbFile(path, parent, dowhat=dowhat)

setup.py

@@ -52,7 +52,7 @@ def read(fname):
         # * Optional: process ipython magics (required import: IPython)
         'jupyter_client',
         'nbformat',
-        'nbconvert',
+        'nbconvert <6',
     # TODO: I think the decision was to go with python/setup.py for this stuff,
     # right? (but if so, how do I specify it's the runtime python version
     # I'm talking aobut, not the buildtime python version?)