Fix a couple of comment typos.

src/library_pthread.js

@@ -121,7 +121,7 @@ var LibraryPThread = {
       if (pthread.worker) pthread.worker.pthread = null;
     },
 
-    // Allocates a the given amount of new web workers and stores them in the pool of unused workers.
+    // Allocates the given amount of new web workers and stores them in the pool of unused workers.
     // onFinishedLoading: A callback function that will be called once all of the workers have been initialized and are
     //                    ready to host pthreads. Optional. This is used to mitigate bug https://bugzilla.mozilla.org/show_bug.cgi?id=1049079
     allocateUnusedWorkers: function(numWorkers, onFinishedLoading) {

src/preamble.js

@@ -497,7 +497,7 @@ function stringToAscii(str, outPtr) {
 }
 Module['stringToAscii'] = stringToAscii;
 
-// Given a pointer 'ptr' to a null-terminated UTF8-encoded string in the a given array that contains uint8 values, returns
+// Given a pointer 'ptr' to a null-terminated UTF8-encoded string in the given array that contains uint8 values, returns
 // a copy of that string as a Javascript String object.
 
 function UTF8ArrayToString(u8Array, idx) {