update README

Author: findmyway

README.md

@@ -68,7 +68,7 @@ If you would like to make some improvements, I'd suggest the following workflow:
 | | [fig_10_3](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_10_3.png), [fig_10_4](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_10_4.png), [fig_10_5](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_10_5.png)| |
 |Chapter11 | [fig_11_2](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_11_2.png) | |
 |Chapter12 | [fig_12_3](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_12_3.png)| Other figures in Chapter12 are not that easy to reproduce by using the Ju.jl package. You may take a try and correct me with a PR.|
-| Chapter13 | [fig_13_1](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_13_1.png), [fig_13_2](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_13_2.png) | Figure_13_2 is a slightly different to the original figure on the book.|
+| Chapter13 | [fig_13_1](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_13_1.png), [fig_13_2](https://raw.githubusercontent.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/master/docs/src/assets/figures/figure_13_2.png) | ~~Figure_13_2 is a slightly different to the original figure on the book.~~ Thanks to Eric Graves's clarification, fixed in [#3](https://github.com/Ju-jl/ReinforcementLearningAnIntroduction.jl/pull/3)|
 
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