use correct value along x-axis
TH1::GetIntegral() function returns array, the i-th element of which equals integral of first i bins (including current i-th bin) normalized over the whole integral. So, the GetIntegral() array elements correspond to bin borders, but not bin centre values, that is why we should use also bin borders for x[i] elements, don't we? Otherwise we will have systematic shift for 0.5 bin width. Especially it's important for continuous-distributed values such as E_psd.