Change config default matcher to IgnoreCase

Default Matcher is set to CaseSensitive when rcfile is given. 
```
echo "a\nb\n" | go run cmd/peco/peco.go
QUERY>                                              IgnoreCase [1/1]
a
b

echo {} > config.json
echo "a\nb\n" | go run cmd/peco/peco.go --rcfile ./config.json
QUERY>                                              CaseSensitive [1/1]
a
b

echo {} > ~/.peco/config.json
echo "a\nb\n" | go run cmd/peco/peco.go
UERY>                                               CaseSensitive [1/1]
a
b
```