did modify gasEstimate according policy

Author: alex78pro

Sources/web3swift/Promises/Promise+Web3+Eth+EstimateGas.swift

@@ -24,7 +24,22 @@ extension web3.Eth {
                     }
                     throw Web3Error.nodeError(desc: "Invalid value from Ethereum node")
                 }
-                return value
+                
+                if let policy = transactionOptions?.gasLimit {
+                    switch policy {
+                    case .automatic:
+                        return value
+                    case .limited(let limitValue):
+                        return limitValue < value ? limitValue: value
+                    case .manual(let exactValue):
+                        return exactValue
+                    case .withMargin:
+                        // MARK: - update value according margin
+                        return value
+                    }
+                } else {
+                    return value
+                }
             }
         } catch {
             let returnPromise = Promise<BigUInt>.pending()