Fix typo "atleast" (#2259)

This isn't really a typo but an issue with bikeshed not leaving a
space at line breaks.  See speced/bikeshed#1470.

Author: rtoy

index.bs

@@ -864,8 +864,7 @@ Methods</h4>
 
 		<pre class=argumentdef for="BaseAudioContext/createBuffer()">
 		numberOfChannels: Determines how many channels the buffer will have. An implementation MUST support at least 32 channels.
-		length: Determines the size of the buffer in sample-frames.  This MUST be at
-			least 1.
+		length: Determines the size of the buffer in sample-frames.  This MUST be at least 1.
 		sampleRate: Describes the sample-rate of the [=linear PCM=] audio data in the buffer in sample-frames per second. An implementation MUST support sample rates in at least the range 8000 to 96000.
 		</pre>
 		<div>