travis: Use short DATESTR for some packages.
travis: Use short DATESTR for some packages.

litex-hub/litex-conda-compilers,SymbiFlow/conda-packages,SymbiFlow/conda-packages,timvideos/conda-misoc-lm32,litex-hub/litex-conda-prog,timvideos/conda-hdmi2usb-packages,timvideos/conda-misoc-lm32,litex-hub/litex-conda-eda,timvideos/conda-hdmi2usb-packages