[css2] Fix typo

See #2132

Author: frivoal

css2/syndata.html

@@ -1454,7 +1454,7 @@ <h3 id="color-units">4.3.6 Colors</h3>
 <p>Values outside the device gamut should be clipped or
 mapped into the gamut when the gamut is known: the red, green,
 and blue values must be changed to fall within the range supported by
-the device. Users agents may perform higher quality mapping of colors
+the device. User agents may perform higher quality mapping of colors
 from one gamut to another. For a typical CRT monitor, whose device
 gamut is the same as sRGB, the four rules below are equivalent:
 </p>

css2/syndata.src

@@ -1407,7 +1407,7 @@ images are expected to carry their own color information.
 <p>Values outside the device gamut should be clipped or
 mapped into the gamut when the gamut is known: the red, green,
 and blue values must be changed to fall within the range supported by
-the device. Users agents may perform higher quality mapping of colors
+the device. User agents may perform higher quality mapping of colors
 from one gamut to another. For a typical CRT monitor, whose device
 gamut is the same as sRGB, the four rules below are equivalent:
 </p>