Fix example usage for `update` with increment expression
Fix example usage for `update` with increment expression

Wrap a symbol by `Sequel.expr()` to perform an increment update
pfarrell/sequel,gferguson-gd/sequel,knut2/sequel,mpalmer/sequel,seeARMS/sequel,yazshel/sequel,seeARMS/sequel,offshore-safety/sequel,yazshel/sequel,t-morgan/sequel,t-morgan/sequel,offshore-safety/sequel,gferguson-gd/sequel,beni55/sequel,nju520/sequel,knut2/sequel,uhoh-itsmaciek/sequel,offshore-safety/sequel,Marketcircle/sequel,davidbegin/sequel,davidbegin/sequel,nicohvi/sequel,nju520/sequel,reubano/sequel,mpalmer/sequel,pfarrell/sequel,nicohvi/sequel,reubano/sequel,beni55/sequel,uhoh-itsmaciek/sequel