Fix binding to context for plugin blocks

lib/plugins/plugin.js

@@ -284,8 +284,8 @@ BookPlugin.prototype.getBlocks = function() {
     return _.mapValues(this.content.blocks || {}, function(block, blockName) {
         block = _.isFunction(block)? { process: block } : block;
 
-        var fn = block.exec;
-        block.exec = function() {
+        var fn = block.process;
+        block.process = function() {
             var ctx = _.extend(pluginCtx(that), this);
 
             return fn.apply(ctx, arguments);

test/plugins.js

@@ -168,11 +168,11 @@ describe('Plugins', function() {
         });
 
         it('should correctly normalize block', function() {
-            blocks.hello.exec({ body: 'World' }).should.equal('Hello World!');
+            blocks.hello.process({ body: 'World' }).should.equal('Hello World!');
         });
 
         it('should correctly set contexts for filter', function() {
-            blocks.testContext.exec({ body: 'Hello' });
+            blocks.testContext.process({ body: 'Hello' });
         });
     });
 });