Fix a Python3-compatibility issue for write_icd_json.py.

I stumbled across this while bringing up the Chromium build
under Python3. The change should allow the code to work under
both 2 and 3 now.

Bug: chromium:1112479
Change-Id: I5ae0cafdd453a12b53a0fa5392ad46cba60f4ed4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/47308
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/src/Vulkan/write_icd_json.py b/src/Vulkan/write_icd_json.py
index 8c7c9f0..a380580 100644
--- a/src/Vulkan/write_icd_json.py
+++ b/src/Vulkan/write_icd_json.py
@@ -24,7 +24,7 @@
     args = parser.parse_args()
 
     with open(args.input) as infile:
-        with open(args.output, 'wb') as outfile:
+        with open(args.output, 'w') as outfile:
             data = json.load(infile)
             data['ICD']['library_path'] = args.library_path
             json.dump(data, outfile)