Convert all fns to block arg syntax.

test/list/map.wren

@@ -1,3 +1,3 @@
 var a = [1, 2, 3]
-var b = a.map(fn (x) x + 1)
+var b = a.map {|x| x + 1 }
 IO.print(b) // expect: [2, 3, 4]

test/list/where.wren

@@ -1,6 +1,6 @@
 var a = [1, 2, 3]
-var b = a.where(fn (x) x > 1)
+var b = a.where {|x| x > 1 }
 IO.print(b) // expect: [2, 3]
 
-var c = a.where(fn (x) x > 10)
+var c = a.where {|x| x > 10 }
 IO.print(c) // expect: []