Voltage across the Current source in a RC circuit
You need to be given or make an assumption about the initial capacitor voltage (at \$t=-1\$).

I would suggest that you perform a separate integral over each time period where the current has a constant slope, such as from \$t=-1\$ to \$t=0\$. The initial condition for each subsequent integral would be the final capacitor voltage for the integral over the previous time interval.