rename invalidateExchangeContract to invalidateContractInstance

src/0x.js.ts

@@ -142,7 +142,7 @@ export class ZeroEx {
      */
     public setProvider(provider: Web3.Provider) {
         this.web3Wrapper.setProvider(provider);
-        this.exchange.invalidateExchangeContract();
+        this.exchange.invalidateContractInstance();
     }
     /**
      * Signs an orderHash and returns it's elliptic curve signature

src/contract_wrappers/exchange_wrapper.ts

@@ -12,7 +12,7 @@ export class ExchangeWrapper extends ContractWrapper {
     constructor(web3Wrapper: Web3Wrapper) {
         super(web3Wrapper);
     }
-    public invalidateExchangeContract() {
+    public invalidateContractInstance() {
         delete this.exchangeContractIfExists;
     }
     public async isValidSignatureAsync(dataHex: string, ecSignature: ECSignature,