refactor: typo fix in maxSessions variable doc string. (#1809)

refactor: typo fix in maxSessions variable doc string.

Author: vi3k6i5

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionOptions.java

@@ -188,7 +188,7 @@ public String[] getValidValues() {
   public static final String OAUTH_TOKEN_PROPERTY_NAME = "oauthToken";
   /** Name of the 'minSessions' connection property. */
   public static final String MIN_SESSIONS_PROPERTY_NAME = "minSessions";
-  /** Name of the 'numChannels' connection property. */
+  /** Name of the 'maxSessions' connection property. */
   public static final String MAX_SESSIONS_PROPERTY_NAME = "maxSessions";
   /** Name of the 'numChannels' connection property. */
   public static final String NUM_CHANNELS_PROPERTY_NAME = "numChannels";