Fixed a bug in dump.hpp that disallowed plus or minus signs after "e".
Fixed a bug in dump.hpp that disallowed plus or minus signs after "e".

stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/math