style: Updated links to Router01 and Router02 docs

The following links were throwing **Page Not Found** errors. On inspection, I noticed that they were pointing to outdated endpoint and hence the error. So, I have updated the links 
```
https://docs.uniswap.org/v2/smart-contracts/router01/
```
to 
```
https://docs.uniswap.org/contracts/v2/reference/smart-contracts/router-01
```

Same goes for the Router02.

Author: consentsam

src/content/developers/tutorials/uniswap-v2-annotated-code/index.md

@@ -905,12 +905,12 @@ The periphery contracts are the API (application program interface) for Uniswap.
 
 ### UniswapV2Router01.sol {#UniswapV2Router01}
 
-[This contract](https://github.com/Uniswap/uniswap-v2-periphery/blob/master/contracts/UniswapV2Router01.sol) has problems, and [should no longer be used](https://uniswap.org/docs/v2/smart-contracts/router01/). Luckily, the periphery contracts are stateless and don't hold any assets, so it is easy to deprecate it and suggest people use the replacement, `UniswapV2Router02`, instead.
+[This contract](https://github.com/Uniswap/uniswap-v2-periphery/blob/master/contracts/UniswapV2Router01.sol) has problems, and [should no longer be used](https://docs.uniswap.org/contracts/v2/reference/smart-contracts/router-01). Luckily, the periphery contracts are stateless and don't hold any assets, so it is easy to deprecate it and suggest people use the replacement, `UniswapV2Router02`, instead.
 
 ### UniswapV2Router02.sol {#UniswapV2Router02}
 
 In most cases you would use Uniswap through [this contract](https://github.com/Uniswap/uniswap-v2-periphery/blob/master/contracts/UniswapV2Router02.sol).
-You can see how to use it [here](https://uniswap.org/docs/v2/smart-contracts/router02/).
+You can see how to use it [here](https://docs.uniswap.org/contracts/v2/reference/smart-contracts/router-02).
 
 ```solidity
 pragma solidity =0.6.6;