doc/developing.ad: replace removed backslash
doc/developing.ad: replace removed backslash

Having two ~s in one block confused doc generation.

R=rsesek@chromium.org

Review URL: https://codereview.chromium.org/1413203002 .

atom/crashpad,chromium/crashpad,atom/crashpad,chromium/crashpad,atom/crashpad,chromium/crashpad