Add 10nF cap on DPPM Power Shield

[mohitbhoite]

When the user plugs in the battery for the first time, the battery charger will fault to short circuit and cut off the power supply to the Photon. This can be overcome by unplugging and plugging back the battery.

To mitigate this issue, the datasheet recommends adding a 1 - 10nF capacitor on the DPPM to delay the short circuit protection to kick in.

[ericyuanyong]

in power shield v220.sch. There is a 10nF capacitor which is parallel with a 30K resistor between DPPM and GND. Turns out currently we product power shield by the gerber of v210 which didnot have that cap.