quote.Get nil pointer dereferencing when asking quote of a inexistent symbol

[pallotron]

Hi,

quote.Get of an inexistent symbol should return a non nil error.
This does not happen....
To repro ask for a quote from a un-existant symbol:

package main

import (
	"fmt"

	"github.com/piquette/finance-go/quote"
)

func main() {
	q, err := quote.Get("FOOAASDADSAS")
	if err != nil {
		panic(err)
	}
	fmt.Printf("RegulardMarketPrice: %# +v", q.RegularMarketPrice)
}

This will panic:

$ go run .
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x50 pc=0x620b2e]

goroutine 1 [running]:
main.main()
        /home/pallotron/projects/example/ticker-quote.go:14 +0x2e
exit status 2
[Exit code 1 @ 10:12:01]

get.Quote should return an error in this case.

[pallotron]

I will send a PR soon.

[pallotron]

PR at #22