Update events doc

Changed the name of the variable because the RTD displays it in green (like the data type or the syntax of the word function), apparently, this is due to the formatting of the RTD text.
https://docs.soliditylang.org/en/latest/contracts.html#events

docs/contracts/events.rst

@@ -93,10 +93,10 @@ The use in the JavaScript API is as follows:
     var ClientReceipt = web3.eth.contract(abi);
     var clientReceipt = ClientReceipt.at("0x1234...ab67" /* address */);
 
-    var event = clientReceipt.Deposit();
+    var depositEvent = clientReceipt.Deposit();
 
     // watch for changes
-    event.watch(function(error, result){
+    depositEvent.watch(function(error, result){
         // result contains non-indexed arguments and topics
         // given to the `Deposit` call.
         if (!error)
@@ -105,7 +105,7 @@ The use in the JavaScript API is as follows:
 
 
     // Or pass a callback to start watching immediately
-    var event = clientReceipt.Deposit(function(error, result) {
+    var depositEvent = clientReceipt.Deposit(function(error, result) {
         if (!error)
             console.log(result);
     });