Update idlelib NEWS for 3.7 (#2089)

Lib/idlelib/NEWS.txt

-What's New in IDLE 3.6.0?
-===========================
-*Release date: 2016-12-16?*
+What's New in IDLE 3.7.0
+Released on 2018-06-18?
+========================
+
+bpo-30290: Help-about: use pep8 names and add tests.
+Increase coverage to 100%.
+Patches by Louie Lu, Cheryl Sabella, and Terry Jan Reedy.
+
+bpo-30303: Add _utest option to textview; add new tests.
+Increase coverage to 100%.
+Patches by Louie Lu and Terry Jan Reedy.
+
+Issue #29071: IDLE colors f-string prefixes (but not invalid ur prefixes).
+
+Issue #28572: Add 10% to coverage of IDLE's test_configdialog.
+Update and augment description of the configuration system.
+
+
+What's New in IDLE 3.6.0
+Released on 2016-12-23
+========================
 
 - Issue #15308: Add 'interrupt execution' (^C) to Shell menu.
   Patch by Roger Serwy, updated by Bayard Randel.