A compound of formula (I) or a salt thereof: wherein R1 represents a five-membered aromatic heterocycle selected from a N- or a C-linked mono- or di-substituted pyrazole, an N- or a C-linked optionally mono- or di-substituted triazole or an N- or a C-linked optionally mono- or di-substituted imidazole, which five-membered aromatic heterocycle may be substituted by one or two of the groups selected a methyl group, an ethyl group, a fluorine atom, a hydroxymethyl group, a 2-hydroxypropan-2-yl group, a trifluoromethyl group, a difluoromethyl group or a fluoromethyl group, except that when R1 represents an N-linked mono- or di-substituted pyrazole, R1 does not represent 3,5-Dimethyl-1H-pyrazol-1-yl, 5-Methyl-1H-pyrazol-1-yl, 5-Ethyl-3-methyl-1H-pyrazol-1-yl, 3,5-Diethyl-1H-pyrazol-1-yl, 4-Fluoro-3,5-dimethyl-1H-pyrazol-1-yl, 3-Methyl-1H-pyrazol-1-yl or 1H-pyrazol-1-yl.