Throw SendGridException on IOException while communicating with SendGrid API.

Fixes #51.

Author: Chris Dinn

src/main/java/com/sendgrid/SendGrid.java

@@ -148,7 +148,7 @@ public SendGrid.Response send(Email email) throws SendGridException {
       HttpResponse res = this.client.execute(httppost);
       return new SendGrid.Response(res.getStatusLine().getStatusCode(), EntityUtils.toString(res.getEntity()));
     } catch (IOException e) {
-      return new SendGrid.Response(500, "Problem connecting to SendGrid");
+      throw new SendGridException(e);
     }
 
   }