Support in-casesensitivity flag in attr selector

This type of selector already is supported by Firefox 47+, Chrome 49+,
and Safari 9.

This fixes #87.

index.js

@@ -181,7 +181,7 @@ function wringValue(prop, value) {
 }
 
 // Unquote attribute selector if possible
-function unquoteAttributeSelector(m, att, con, val) {
+function unquoteAttributeSelector(m, att, con, val, oq, flag) {
   if (!con || !val) {
     return `[${att}]`;
   }
@@ -193,6 +193,10 @@ function unquoteAttributeSelector(m, att, con, val) {
     val = `${quote}${val}${quote}`;
   }
 
+  if (flag === "i") {
+    val = `${val} i`;
+  }
+
   return `[${att}${con}${val}]`;
 }
 

lib/regexp.js

@@ -51,7 +51,7 @@ re.propertyMultipleValues = /^(margin|padding|border-(color|radius|spacing|style
 re.quotedString = /("|')?(.*)\1/;
 
 // [class = "foo"], [class ~= "foo"], [class |= "foo"], [class ^= "foo"], [class $= "foo"], [class *= "foo"]
-re.selectorAtt = /\[\s*(.*?)(?:\s*([~|^$*]?=)\s*(("|').*\4|.*?[^\\]))?\s*\]/g;
+re.selectorAtt = /\[\s*(.*?)(?:\s*([~|^$*]?=)\s*(("|').*\4|.*?[^\\]))?\s*(i)?\]/g;
 
 // p > a, p + a, p ~ a
 re.selectorCombinators = /\s+((\\?)[>+~])\s+/g;

test/expected/issue87.css

@@ -0,0 +1 @@
+[class=foo i]{display:block}[class="bar baz" i]{display:block}

test/fixtures/issue87.css

@@ -0,0 +1,8 @@
+[class = "foo" i] {
+  display: block;
+}
+
+[class = "bar baz"
+i] {
+  display: block;
+}