Merge pull request #102 from caternuson/iss100

Update begin() to fix memory leak.

Author: ladyada

Adafruit_ADS1X15.cpp

@@ -63,6 +63,9 @@ Adafruit_ADS1115::Adafruit_ADS1115() {
 */
 /**************************************************************************/
 bool Adafruit_ADS1X15::begin(uint8_t i2c_addr, TwoWire *wire) {
+  if (m_i2c_dev) {
+    delete m_i2c_dev;
+  }
   m_i2c_dev = new Adafruit_I2CDevice(i2c_addr, wire);
   return m_i2c_dev->begin();
 }