StringUtils: Fix a typo

It was meant to be less-equal, like in case of lowercase.

Amends d91d402853

Change-Id: I0c47da1a5a1da1638a66d28ac7ef3830bf733371
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/stringutils.cpp

@@ -110,7 +110,7 @@ enum class Base { Dec, Hex };
 
 static bool isHex(const QChar &c)
 {
-    return (c >= 'a' && c <= 'f') || (c >= 'A' && c < 'F');
+    return (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');
 }
 
 static bool isDigit(const QChar &c, Base base)