Pipe output directly to str and avoid additional memory allocations

Currently, there are lots of examples of code like this,
```
str << ('<tag ' << foo << ' ' << bar << '/>')
```
which create the string for the tag in memory before piping to str.

We can avoid creating all of these intermediate strings by dropping
the paranthesis and piping directly to str.

This relies on the `str` passed around to handle lots of small
appends. This is a problem when using RubyZip, but that is solved
in the next commit.

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/axlsx/drawing/line_series.rb b/lib/axlsx/drawing/line_series.rb
index 42c86873..bbd3957e 100644
--- a/lib/axlsx/drawing/line_series.rb
+++ b/lib/axlsx/drawing/line_series.rb
@@ -75,11 +75,11 @@ module Axlsx
       super(str) do
         if color
           str << '<c:spPr><a:solidFill>'
-          str << (+'<a:srgbClr val="' << color << '"/>')
+          str << '<a:srgbClr val="' << color << '"/>'
           str << '</a:solidFill>'
           str << '<a:ln w="28800">'
           str << '<a:solidFill>'
-          str << (+'<a:srgbClr val="' << color << '"/>')
+          str << '<a:srgbClr val="' << color << '"/>'
           str << '</a:solidFill>'
           str << '</a:ln>'
           str << '<a:round/>'
@@ -94,7 +94,7 @@ module Axlsx
 
         @labels.to_xml_string(str) unless @labels.nil?
         @data.to_xml_string(str) unless @data.nil?
-        str << (+'<c:smooth val="' << ((smooth) ? '1' : '0') << '"/>')
+        str << '<c:smooth val="' << ((smooth) ? '1' : '0') << '"/>'
       end
     end