Floating point literals should accept unsigned exponents

[apiarian]

According to https://golang.org/ref/spec#Floating-point_literals the + or - bit after the E is optional. Should the line below just be changed to say something like [\+\-]?

language-go/grammars/go.cson

Line 128 in f7c6ca6

'match': '(\\.\\d+([Ee][\-\+]\\d+)?i?)\\b|\\b\\d+\\.\\d*(([Ee][\-\+]\\d+)?i?\\b)?'