remove Python 2.6 from build matrix
remove Python 2.6 from build matrix

patrys/opbeat_python,beniwohli/apm-agent-python,beniwohli/apm-agent-python,patrys/opbeat_python,patrys/opbeat_python,patrys/opbeat_python,beniwohli/apm-agent-python,beniwohli/apm-agent-python