Fix a code typo in readme.md (#136)

* Fix a code typo in README.md

* revert unrelated change

Author: keefo

README.md

@@ -179,7 +179,7 @@ lineGraph2.plotLabel.yLabel = "Y-AXIS"
 lineGraph2.plotLineThickness = 3.0
 
 subplot.plots = [lineGraph1, lineGraph2]
-subPlot.drawGraphAndOutput(fileName: "subPlotsHorizontallyStacked", renderer: agg_renderer)
+subplot.drawGraphAndOutput(fileName: "subPlotsHorizontallyStacked", renderer: agg_renderer)
 ```
 
 <img src="Tests/SwiftPlotTests/Reference/agg/_03_sub_plot_horizontally_stacked_line_chart.png" width="500">
@@ -488,4 +488,4 @@ If you want to contribute to improve this library, please read our [guidelines](
 1. Maxim Shemanarev : The AGG library is directly used to render plots.
 2. [Lode Vandevenne](https://github.com/lvandeve) : The lodepng library is directly used to encode PNG images.
 3. [The FreeType Project](https://www.freetype.org) : AGG uses FreeType to draw text.
-4. [Brad Larson](https://github.com/BradLarson) and [Marc Rasi](https://github.com/marcrasi) for their invaluable guidance.
+4. [Brad Larson](https://github.com/BradLarson) and [Marc Rasi](https://github.com/marcrasi) for their invaluable guidance.