fix typo

参数theta应该减去正则项，而不是加，目测是因为少了个括号。但是下文逻辑回归部分写的没错。所以直接复制了下文逻辑回归的梯度下降部分公式。合并前请检查下

markdown/week3.md

@@ -494,13 +494,14 @@ $J\left( \theta  \right)=\frac{1}{2m}\sum\limits_{i=1}^{m}{[({{({h_\theta}({{x}^
 
 $Repeat$  $until$  $convergence${
 
-​       ${\theta_0}:={\theta_0}-a\frac{1}{m}\sum\limits_{i=1}^{m}{({h_\theta}({{x}^{(i)}})-{{y}^{(i)}})x_{0}^{(i)}}$ 
+​       ${\theta_0}:={\theta_0}-a\frac{1}{m}\sum\limits_{i=1}^{m}{(({h_\theta}({{x}^{(i)}})-{{y}^{(i)}})x_{0}^{(i)}})$ 
 
-​       ${\theta_j}:={\theta_j}-a\frac{1}{m}\sum\limits_{i=1}^{m}{({h_\theta}({{x}^{(i)}})-{{y}^{(i)}})x_{j}^{\left( i \right)}}+\frac{\lambda }{m}{\theta_j}$ 
+​       ${\theta_j}:={\theta_j}-a\frac{1}{m}\sum\limits_{i=1}^{m}{(({h_\theta}({{x}^{(i)}})-{{y}^{(i)}})x_{j}^{\left( i \right)}}+\frac{\lambda }{m}{\theta_j})$ 
 
-​                    }
+​                                            $for$ $j=1,2,...n$
+
+​                       }
 
-$Repeat$
 
 对上面的算法中$ j=1,2,...,n$ 时的更新式子进行调整可得：