patch 8.0.0171: JS style JSON does not support single quotes

Problem:    JS style JSON does not support single quotes.
Solution:   Allow for single quotes. (Yasuhiro Matsumoto, closes #1371)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index b3c7323..a53b5d2 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -5229,6 +5229,7 @@
 js_decode({string})					*js_decode()*
 		This is similar to |json_decode()| with these differences:
 		- Object key names do not have to be in quotes.
+		- Strings can be in single quotes.
 		- Empty items in an array (between two commas) are allowed and
 		  result in v:none items.