Allow trailing semicolon (;) after field values.

For example:
message Example {
  option (custom) = {
    value1: "value1";
    value2: "value2"
  };
}
diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
index eb022ea..bdfb26b 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
@@ -225,10 +225,10 @@
   SimpleValueField | ComplexValueField;
 
 SimpleValueField:
-  name=FieldName ':' value=SimpleValueLink;
+  name=FieldName ':' value=SimpleValueLink ';'?;
 
 ComplexValueField:
-  name=FieldName ':'? values=ComplexValue;
+  name=FieldName ':'? values=ComplexValue ';'?;
 
 FieldName:
   NormalFieldName | ExtensionFieldName;