rename conditional to if expression

lib/ast/expression.rb

@@ -34,7 +34,7 @@ end
 
 require_relative "basic_expressions"
 require_relative "compound_expressions"
-require_relative "conditional_expression"
+require_relative "if_expression"
 require_relative "while_expression"
 require_relative "function_expression"
 require_relative "operator_expressions"

lib/ast/if_expression.rb

@@ -1,5 +1,5 @@
 module Ast
-  class ConditionalExpression < Expression
+  class IfExpression < Expression
     attr_reader  :cond, :if_true, :if_false
     def initialize cond, if_true, if_false
       @cond, @if_true, @if_false = cond, if_true, if_false