Pass through octal and binary literals as-is

See coffeescript6/discuss#45

src/lexer.coffee

@@ -195,15 +195,16 @@ exports.Lexer = class Lexer
     number = match[0]
     lexedLength = number.length
 
-    if /^0[BOX]/.test number
-      @error "radix prefix in '#{number}' must be lowercase", offset: 1
-    else if /E/.test(number) and not /^0x/.test number
-      @error "exponential notation in '#{number}' must be indicated with a lowercase 'e'",
-        offset: number.indexOf('E')
-    else if /^0\d*[89]/.test number
-      @error "decimal literal '#{number}' must not be prefixed with '0'", length: lexedLength
-    else if /^0\d+/.test number
-      @error "octal literal '#{number}' must be prefixed with '0o'", length: lexedLength
+    switch
+      when /^0[BOX]/.test number
+        @error "radix prefix in '#{number}' must be lowercase", offset: 1
+      when /^(?!0x).*E/.test number
+        @error "exponential notation in '#{number}' must be indicated with a lowercase 'e'",
+          offset: number.indexOf('E')
+      when /^0\d*[89]/.test number
+        @error "decimal literal '#{number}' must not be prefixed with '0'", length: lexedLength
+      when /^0\d+/.test number
+        @error "octal literal '#{number}' must be prefixed with '0o'", length: lexedLength
 
     numberValue = number