No data from U-Blox Neo-6M
It isn't enough to power the module with 3.3V. You also have to level-shift the Arduino's 5V TX signal to 3.3V that is acceptable by the GPS module's RX pin, using a 1:2 voltage divider. 



You should also know that the Arduino's 3.3 V pin can't source more than 50 mA; your module's current draw may sometimes exceed this limit (max is 67 mA). Instead, connect the Arduino's 5 V pin (which can source up to 500 mA) to the VCC of the GPS module through an LM1117T 3.3 V regulator:



The input goes the Arduino 5V pin and the output goes to the NEO-6M VCC. Connect all GNDs together.

Then run a basic sketch like this:

#include "SoftwareSerial.h"

SoftwareSerial gps(4,3);

void setup(){
  Serial.begin(9600);
  gps.begin(9600);
}

void loop(){
  while (gps.available())
    Serial.write(gps.read());
}


This will basically make the Arduino grab any NMEA data sent by the NEO-6M and forward it to your PC's serial monitor. If you receive legible data, it means you've established comms with the module. You can then upload your original sketch.