* Update gsn_advanced.adoc

Line 15 - where it says, "prevent malicious users from spending the transactions subsidy", with transactions subsidy, is it supposed to be possessive "transaction's subsidy" or is the plural in the wrong place "transaction subsidies"?

Line 176 - where it says "or it is not allowed to spend that amount". Is IT referring to the sender/person or the tx? If IT refers to a person, then change to "or they are not allowed..." for gender neutral.

Line 213 - Where it says, "Please not how the gas cost estimation", a verb is missing, please what?

* Update gsn_advanced.adoc

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