parse negative integers in YAML

Author: ddsharpe

core/src/main/antlr4/oracle/weblogic/deploy/yaml/Yaml.g4

@@ -260,7 +260,7 @@ fragment FALSE_TEXT
     ;
 
 fragment INT_TEXT
-    : [1-9] [0-9]*
+    : '-'? [1-9] [0-9]*
     ;
 
 fragment FLOAT_TEXT