Should only support UTF-8

For the same reasons as BurntSushi/xsv#42 we
should only support UTF-8 and other encodings should be converted to
UTF-8 before processing.

spec/csv-to-json_spec.cr

@@ -94,15 +94,13 @@ describe Csv::To::Json do
         out_io.to_s.should contain(%([\n{"field 1":"あ"}\n]\n))
       end
 
-      it "will parse bad_data.tsv fixture" do
-        in_io = File.open("spec/fixtures/bad_data.tsv")
-        in_io.set_encoding(encoding: "latin1")
+      it "will throw exception for latin1 encoded file" do
+        in_io = File.open("spec/fixtures/latin1.tsv")
         out_io = IO::Memory.new()
 
-        Csv::To::Json.run(in_io, out_io)
-
-        out_io.seek(0)
-        out_io.to_s.should contain(%([\n{"field 1":"Associação Paulista de Cirurgiões-Den"}\n]\n))
+        expect_raises(InvalidByteSequenceError) do
+          Csv::To::Json.run(in_io, out_io)
+        end
       end
 
       it "will parse \u0041 char" do

src/csv-to-json.cr

@@ -7,8 +7,6 @@ module Csv::To::Json
   def self.run(in_io, out_io, options = {} of Symbol => String)
     STDIN.blocking = true
 
-    # in_io.set_encoding(encoding: "UTF-8", invalid: :skip)
-
     empty_value_replace_char = options.fetch(:empty_value_replace_char, "")
     tail = options.delete :tail
     delimiter = options.fetch(:delimiter, ',').as(Char)