mv stream.stream > stream.name in nbformat.v4

matches message spec

IPython/nbformat/v4/nbbase.py

@@ -44,7 +44,7 b' def new_output(output_type, mime_bundle=None, **kwargs):'
     # populate defaults:
     output.setdefault('metadata', NotebookNode())
     if output_type == 'stream':
-        output.setdefault('stream', 'stdout')
+        output.setdefault('name', 'stdout')
         output.setdefault('text', '')
     validate(output, output_type)
     return output

IPython/nbformat/v4/nbformat.v4.schema.json

@@ -250,15 +250,15 b''
             "description": "Stream output from a code cell.",
             "type": "object",
             "additionalProperties": false,
-            "required": ["output_type", "metadata", "stream", "text"],
+            "required": ["output_type", "metadata", "name", "text"],
             "properties": {
                 "output_type": {
                     "description": "Type of cell output.",
                     "enum": ["stream"]
                 },
                 "metadata": {"$ref": "#/definitions/misc/output_metadata"},
-                "stream": {
-                    "description": "The stream type/destination.",
+                "name": {
+                    "description": "The name of the stream (stdout, stderr).",
                     "type": "string"
                 },
                 "text": {

IPython/nbformat/v4/tests/nbexamples.py

@@ -91,7 +91,7 b' cells.append(new_code_cell('
         text='foo\rbar\r\n'
     ),new_output(
         output_type=u'stream',
-        stream='stderr',
+        name='stderr',
         text='\rfoo\rbar\n'
     )]
 ))

IPython/nbformat/v4/tests/test_nbbase.py

@@ -55,8 +55,10 b' def test_empty_display_data():'
     nt.assert_equal(output.output_type, 'display_data')
 
 def test_empty_stream():
-    output = new_output('stream', stream='stdout', text='')
+    output = new_output('stream')
     nt.assert_equal(output.output_type, 'stream')
+    nt.assert_equal(output.name, 'stdout')
+    nt.assert_equal(output.text, '')
 
 def test_empty_execute_result():
     output = new_output('execute_result', prompt_number=1)
@@ -103,3 +105,8 b' def test_code_cell_with_outputs():'
     er = cell.outputs[-1]
     nt.assert_equal(er.prompt_number, 10)
     nt.assert_equal(er['output_type'], 'execute_result')
+
+def test_stream():
+    output = new_output('stream', name='stderr', text='hello there')
+    nt.assert_equal(output.name, 'stderr')
+    nt.assert_equal(output.text, 'hello there')