minor wording changes

Author: serggl

README.md

@@ -122,15 +122,15 @@ Simply call static method `BillingProcessor.isIabServiceAvailable()`:
         // continue
     }
 ```
-Please take a note that calling to `BillingProcessor.isIabServiceAvailable()` (only checks Play Market app installed or not) is not enough because there might be a case when it returns true but still payment won't success. Therefore, it's better to
-call to method `isOnTimePurchaseSupported()` after initializing `BillingProcessor`:
+Please notice that calling `BillingProcessor.isIabServiceAvailable()` (only checks Play Market app installed or not) is not enough because there might be a case when it returns true but still payment won't succeed.
+Therefore, it's better to call `isOneTimePurchaseSupported()` after initializing `BillingProcessor`:
 ```java
-    boolean isOneTimePurchaseSupported = billingProcessor.isOnTimePurchaseSupported();
+    boolean isOneTimePurchaseSupported = billingProcessor.isOneTimePurchaseSupported();
     if(isOneTimePurchaseSupported) {
         // launch payment flow
     }
 ```
-or call to method `isSubscriptionUpdateSupported()` for checking update subcription usecase:
+or call `isSubscriptionUpdateSupported()` for checking update subscription use case:
 ```java
     boolean isSubsUpdateSupported = billingProcessor.isSubscriptionUpdateSupported();
     if(isSubsUpdateSupported) {

library/src/main/java/com/anjlab/android/iab/v3/BillingProcessor.java

@@ -74,7 +74,7 @@ public interface IBillingHandler {
 	private BillingCache cachedSubscriptions;
 	private IBillingHandler eventHandler;
 	private String developerMerchantId;
-	private boolean isOneTimePurchaseSupported;
+	private boolean isOneTimePurchasesSupported;
 	private boolean isSubsUpdateSupported;
 
 	private class HistoryInitializationTask extends AsyncTask<Void, Void, Boolean>
@@ -235,16 +235,16 @@ public boolean subscribe(Activity activity, String productId, String developerPa
 	}
 
 	public boolean isOnTimePurchaseSupported(){
-		if (isOneTimePurchaseSupported)
+		if (isOneTimePurchasesSupported)
 			return true;
 
 		try {
 			int response = billingService.isBillingSupported(Constants.GOOGLE_API_VERSION, contextPackageName, Constants.PRODUCT_TYPE_MANAGED);
-			isOneTimePurchaseSupported = response == Constants.BILLING_RESPONSE_RESULT_OK;
+			isOneTimePurchasesSupported = response == Constants.BILLING_RESPONSE_RESULT_OK;
 		} catch (RemoteException e) {
 			e.printStackTrace();
 		}
-		return isOneTimePurchaseSupported;
+		return isOneTimePurchasesSupported;
 	}
 
 	public boolean isSubscriptionUpdateSupported() {