fix typo: an active -> active

Author: SidestreamSweatyPumpkin

contracts/bonding/BondingManager.sol

@@ -923,7 +923,7 @@ contract BondingManager is ManagerProxyTarget, IBondingManager {
     ) private whenSystemNotPaused currentRoundInitialized autoCheckpoint(_transcoder) {
         uint256 currentRound = roundsManager().currentRound();
 
-        require(isActiveTranscoder(_transcoder), "transcoder must be an active");
+        require(isActiveTranscoder(_transcoder), "transcoder must be active");
         require(
             transcoders[_transcoder].lastRewardRound != currentRound,
             "caller has already called reward for the current round"

test/unit/BondingManager.js

@@ -5474,7 +5474,7 @@ describe("BondingManager", () => {
         it("should fail if caller is not a transcoder", async () => {
             await expect(
                 bondingManager.connect(nonTranscoder).reward()
-            ).to.be.revertedWith("transcoder must be an active")
+            ).to.be.revertedWith("transcoder must be active")
         })
 
         it("should fail if caller is registered but not an active transcoder yet in the current round", async () => {
@@ -5484,7 +5484,7 @@ describe("BondingManager", () => {
             )
             await expect(
                 bondingManager.connect(transcoder).reward()
-            ).to.be.revertedWith("transcoder must be an active")
+            ).to.be.revertedWith("transcoder must be active")
         })
 
         it("should fail if caller already called reward during the current round", async () => {