docs: correct the missing sentence in animation

Fixed missing word to complete missing sentence in animation docs.

aio/content/guide/transition-and-triggers.md

@@ -227,7 +227,7 @@ The code for this color change might look like this.
 
 ### Offset
 
-Keyframes include an *offset* that defines the point in the animation where each style change occurs. Offsets are relative measures from zero to one, marking the beginning and end of the animation, respectively and should be applied to each of keyframe's steps if used at least once.
+Keyframes include an *offset* that defines the point in the animation where each style change occurs. Offsets are relative measures from zero to one, marking the beginning and end of the animation, respectively and should be applied to each of the keyframe's steps if used at least once.
 
 Defining offsets for keyframes is optional. If you omit them, evenly spaced offsets are automatically assigned. For example, three keyframes without predefined offsets receive offsets of 0, 0.5, and 1. Specifying an offset of 0.8 for the middle transition in the above example might look like this.