Use rstrip for chomp

Performance is than the regex in most cases. If a large portion of the
end of the string is newlines then a regex could be more performant.

Author: omus

src/BlockScalars.jl

@@ -31,9 +31,9 @@ function block(str::AbstractString, block_scalar::AbstractString="")
     end
 
     if chomp == 'c'
-        str = replace(str, r"\n+$" => "\n")
+        str = rstrip(str, '\n') * '\n'
     elseif chomp == 's'
-        str = replace(str, r"\n+$" => "")
+        str = rstrip(str, '\n')
     elseif chomp != 'k'
         throw(ArgumentError("Unknown block chomping indicator: $(repr(chomp))"))
     end