[basic.fundamental] Use correct number; "are", not "is".

Author: tkoeppe

source/basic.tex

@@ -5016,7 +5016,7 @@
 \end{note}
 Except as specified in \ref{basic.extended.fp},
 the object and value representations and accuracy of operations
-of floating-point types is \impldef{representation of floating-point types}.
+of floating-point types are \impldef{representation of floating-point types}.
 
 \pnum
 Integral and floating-point types are collectively