Account for '-' as an operator

For syntax purposes it's part of the number, but it looks better when
highlighted as an operator.

queries/highlights.scm

@@ -5,6 +5,8 @@
 
 ; Operators {{{
 (operator) @operator
+
+(integer_literal ("-") @operator)
 ; }}}
 
 ; Literal {{{

test/highlight/litterals.bp

@@ -2,7 +2,7 @@ foo = 0
 //    ^ number
 
 foo = -42
-//    ^ number
+//     ^ number
 
 foo = true
 //    ^ boolean

test/highlight/operators.bp

@@ -5,4 +5,5 @@ foo += 1
 //  ^ operator
 
 foo = -1 + 2
+//    ^ operator
 //       ^ operator