Support for unicode characters starting with \U

src/main/java/com/moandjiezana/toml/StringConverter.java

@@ -9,7 +9,7 @@ import java.util.regex.Pattern;
 class StringConverter implements ValueConverter {
   
   static final StringConverter STRING_PARSER = new StringConverter();
-  private static final Pattern UNICODE_REGEX = Pattern.compile("\\\\u(.*)");
+  private static final Pattern UNICODE_REGEX = Pattern.compile("\\\\[uU](.*)");
 
   @Override
   public boolean canConvert(String s) {

src/test/java/com/moandjiezana/toml/StringTest.java

@@ -77,6 +77,7 @@ public class StringTest {
     Toml toml = new Toml().parse(new File(getClass().getResource("should_support_special_characters_in_strings.toml").getFile()));
 
     assertEquals("more or less ±", toml.getString("unicode_key"));
+    assertEquals("more or less ±", toml.getString("unicode_key_uppercase"));
   }
 
   @Test(expected = IllegalStateException.class)

src/test/resources/com/moandjiezana/toml/should_support_special_characters_in_strings.toml

@@ -1,2 +1,3 @@
 key = "\" \t \n \r \\ \/ \b \f"
 unicode_key = "more or less \u00B1"
+unicode_key_uppercase = "more or less \U00B1"