Update ThirdPartyNoticeText to include KhronosGroup copyright notice for WebGL.

Licence added in KhronosGroup/WebGL#2674
WebGL spec used in generating the library as of: microsoft/TypeScript-DOM-lib-generator#533

Author: mhegazy

ThirdPartyNoticeText.txt

@@ -164,5 +164,30 @@ For purposes of this definition, the normative portions of the Specification sha
 I am encouraged to provide a contact from which licensing information can be obtained and other relevant licensing information. Any such information will be made publicly available. 
 10.8. You or Your. �You,� �you,� or �your� means any person or entity who exercises copyright or patent rights granted under this Agreement, and any person that person or entity controls.
 
+-------------------------------------------------------------------------------------
+
+------------------- WebGL -----------------------------
+Copyright (c) 2018 The Khronos Group Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and/or associated documentation files (the
+"Materials"), to deal in the Materials without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Materials, and to
+permit persons to whom the Materials are furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be included
+in all copies or substantial portions of the Materials.
+
+THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+MATERIALS OR THE USE OR OTHER DEALINGS IN THE MATERIALS.
+------------------------------------------------------
+
 ------------- End of ThirdPartyNotices ------------------------------------------- */