linter: fix FieldNameRule allowing uppercase letter after _ at start
diff --git a/linter/src/main/java/org/apache/royale/linter/rules/FieldNameRule.java b/linter/src/main/java/org/apache/royale/linter/rules/FieldNameRule.java
index 68c26a0..a786956 100644
--- a/linter/src/main/java/org/apache/royale/linter/rules/FieldNameRule.java
+++ b/linter/src/main/java/org/apache/royale/linter/rules/FieldNameRule.java
@@ -41,7 +41,7 @@
  * Check that field names match a specific pattern.
  */
 public class FieldNameRule extends LinterRule {
-	public static final Pattern DEFAULT_NAME_PATTERN = Pattern.compile("^[_a-z][a-zA-Z0-9]*$");
+	public static final Pattern DEFAULT_NAME_PATTERN = Pattern.compile("^_?[a-z][a-zA-Z0-9]*$");
 
 	@Override
 	public Map<ASTNodeID, NodeVisitor> getNodeVisitors() {