fix off by one index in parse example (#373)

Author: FajitaOfTreason

streamerbot/2.guide/03.variables.md

@@ -180,13 +180,13 @@ Fetches the value of the argument named by `parse`'s parameter, which itself can
 // Same results as %user%
 $parse(user)$
 
-// First, Set Argument %i% to 1
+// First, Set Argument %i% to 0
 $parse(line%i%)$
-// ==> returns value of %line1% (the first line of the file)
+// ==> returns value of %line0% (the first line of the file)
 
-// Set Argument %i% to $math(%i%+1)$ (i.e., 2)
+// Set Argument %i% to $math(%i% + 1)$ (i.e., 1)
 $parse(line%i%)$
-// ==> returns value of %line2% (the second line of the file)
+// ==> returns value of %line1% (the second line of the file)
 ```
 ::tip
 `%arguments%` and `~persistedVariables~` will be parsed in `parse`'s parameter, but not other `$inline()$` functions. If you wish to use a function, then set another argument to the output of the function, and use that argument in the `parse` instead.