Fix IsolationLevel enum values (#1098)

Author: mhowlett

src/Confluent.Kafka/Config.cs

@@ -31,8 +31,10 @@ public class Config : IEnumerable<KeyValuePair<string, string>>
         {
             { "saslplaintext", "sasl_plaintext" },
             { "saslssl", "sasl_ssl" },
-            { "consistentrandom", "consistent_random"},
-            { "murmur2random", "murmur2_random"}
+            { "consistentrandom", "consistent_random" },
+            { "murmur2random", "murmur2_random" },
+            { "readcommitted", "read_committed" },
+            { "readuncommitted", "read_uncommitted" }
         };
 
         /// <summary>

test/Confluent.Kafka.UnitTests/Consumer.cs

@@ -25,7 +25,7 @@ namespace Confluent.Kafka.UnitTests
     public class ConsumerTests
     {
         [Fact]
-        public void Constuctor()
+        public void Constructor()
         {
             // Throw exception if 'group.id' is not set in config and ensure that exception
             // mentions 'group.id'.
@@ -63,6 +63,28 @@ public void Constuctor()
             Assert.Contains("range", e.Message);
         }
 
+        [Fact]
+        public void Constructor_ConsumerTxn()
+        {
+            // should not throw
+            using (var c = new ConsumerBuilder<byte[], byte[]>(new ConsumerConfig
+                {
+                    BootstrapServers = "localhost:666",
+                    GroupId = Guid.NewGuid().ToString(),
+                    IsolationLevel = IsolationLevel.ReadCommitted
+                }).Build())
+            { }
+
+            // should not throw
+            using (var c = new ConsumerBuilder<byte[], byte[]>(new ConsumerConfig
+                {
+                    BootstrapServers = "localhost:666",
+                    GroupId = Guid.NewGuid().ToString(),
+                    IsolationLevel = IsolationLevel.ReadUncommitted
+                }).Build())
+            { }
+        }
+
         private static ConsumerConfig CreateValidConfiguration()
         {
             return new ConsumerConfig