Fix spelling of undoableIrreversibleCheckpoint

Author: Josh Dover

Diff for: README.md

@@ -31,7 +31,7 @@ Reducers can optionally provide a `changeDetector` function to override what cha
 
 Flags on actions can affect the behavior of the undo history state:
 - `undoableHistoryCheckpoint`: Marks when the next state should be considered a checkpoint in the undo history
-- `undoableIrreversableCheckpoint`: Marks when the next state should clear any undo history. Typically used if related
+- `undoableIrreversibleCheckpoint`: Marks when the next state should clear any undo history. Typically used if related
 state in another system (eg. a backend service) cannot be reversed.
 
 ## Example Usage

Diff for: src/Undoable.js

@@ -86,7 +86,7 @@ export default function Undoable(reducers) {
 
 			// New states can only be pushed into the history if anything we care about actually changed.
 			if (anyChanged) {
-				if (action.undoableIrreversableCheckpoint) {
+				if (action.undoableIrreversibleCheckpoint) {
 					return {
 						past:    [nextState],  // irreversible checkpoints should clear out history
 						present: nextState,

Diff for: test/Undoable.test.js

@@ -102,7 +102,7 @@ describe('Undoable', () => {
 			});
 		});
 
-		context('when undoableIrreversableCheckpoint is true', () => {
+		context('when undoableIrreversibleCheckpoint is true', () => {
 			let nextState;
 
 			beforeEach(() => {
@@ -111,7 +111,7 @@ describe('Undoable', () => {
 					present: { test: 1 },
 					future: [{ something: true }]
 				}, {});
-				nextState = UndoableReducer(initialState, { type: TEST_ACTION, undoableIrreversableCheckpoint: true })
+				nextState = UndoableReducer(initialState, { type: TEST_ACTION, undoableIrreversibleCheckpoint: true })
 			});
 
 			it('sets the present', () => expect(nextState.present).to.deep.equal({ test: 2 }));