With attiny cores other than mine, the Wire library doesn't work - you need to use a different library made specifically for hardware on the attiny (which is a USI, not master/slave TWI like the normal ATmega chips have), and then modify the adafruit library to use that library.
Or, you can just use my ATTinyCore, which provides a version of Wire.h which transparently selects the correct implementation of I2C to use for the selected chip, so you CAN do what you're doing and expect it to work without changing anything in the sketch or modifying the library.