Minor typo in expm1 comment

`exp(+-inf)={inf, 0}`, so...

Author: pkofod

src/s_expm1.c

@@ -147,7 +147,7 @@ expm1(double x)
 		    GET_LOW_WORD(low,x);
 		    if(((hx&0xfffff)|low)!=0)
 		         return x+x; 	 /* NaN */
-		    else return (xsb==0)? x:-1.0;/* exp(+-inf)={inf,-1} */
+		    else return (xsb==0)? x:-1.0;/* exp(+-inf)-1={inf,-1} */
 	        }
 	        if(x > o_threshold) return huge*huge; /* overflow */
 	    }