update exercise links to /crytic/ (#38)

Author: rmi7

program-analysis/README.md

@@ -73,9 +73,9 @@ The broad areas that are frequently relevant for smart contracts include:
 Component | Tools | Examples
 --- | --- | --- |
 State machine | Echidna, Manticore | 
-Access control | Slither, Echidna, Manticore | [Slither exercise 2](https://github.com/trailofbits/building-secure-contracts/blob/master/program-analysis/slither/exercise2.md), [Echidna exercise 2](https://github.com/trailofbits/building-secure-contracts/blob/master/program-analysis/echidna/Exercise-2.md)
-Arithmetic operations | Manticore, Echidna | [Echidna exercise 1](https://github.com/trailofbits/building-secure-contracts/blob/master/program-analysis/echidna/Exercise-1.md), [Manticore exercises 1 - 3](https://github.com/trailofbits/building-secure-contracts/tree/master/program-analysis/manticore/exercises)
-Inheritance correctness | Slither | [Slither exercise 1](https://github.com/trailofbits/building-secure-contracts/blob/master/program-analysis/slither/exercise1.md)
+Access control | Slither, Echidna, Manticore | [Slither exercise 2](https://github.com/crytic/building-secure-contracts/blob/master/program-analysis/slither/exercise2.md), [Echidna exercise 2](https://github.com/crytic/building-secure-contracts/blob/master/program-analysis/echidna/Exercise-2.md)
+Arithmetic operations | Manticore, Echidna | [Echidna exercise 1](https://github.com/crytic/building-secure-contracts/blob/master/program-analysis/echidna/Exercise-1.md), [Manticore exercises 1 - 3](https://github.com/crytic/building-secure-contracts/tree/master/program-analysis/manticore/exercises)
+Inheritance correctness | Slither | [Slither exercise 1](https://github.com/crytic/building-secure-contracts/blob/master/program-analysis/slither/exercise1.md)
 External interactions | Manticore, Echidna | 
 Standard conformance | Slither, Echidna, Manticore | [`slither-erc`](https://github.com/crytic/slither/wiki/ERC-Conformance)