ATTINY85 interrupt confusion
There are several things to consider:


The only pin that can be configured for a specific edge change is pin 7, which is PB2. So, your pushbutton should be connected to that pin.
It would be a good practice to pull this pin to ground with a 10k resistor, to make sure it is not floating (i.e. can not make a high on its own).
Set the bit 6 of the GIMSK register to 1 to enable INT0.
Set bits [1:0] of the MCUCR regiter to 11 to generate the interrupt only on the rising edge. 
Set bit 0 of DDRB register to 1 to make it output. That is, PB0 pin would be the output.
Change the interrupt ISR(PCINT0_vect) to ISR(INT0_vect). There is a difference between PCINT0 and INT0.
You can toggle the pin PB0 in your ISR as follows: PORTB = PORTB ^ 0x01
It is not a good practice to have a delay in the ISR
It would be good to implement a de-bounce subrountine to make sure that when you press the button, the INT0 triggers only once.