Minor correction in consequence of the drop of QT2's obsolete QVector class.

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>

kstars/README.planetmath

@@ -64,7 +64,7 @@ The A/B/C constants are stored hierarchically:
  + The A,B,C values for a single term in an s(N) sum are stored in an
    OrbitData object.
  + The list of OrbitData objects that compose a single s(N) sum is
-   stored in a QVector (recall, this can have up to hundreds of elements).
+   stored in a QPtrVector (recall, this can have up to hundreds of elements).
  + The six s(N) sums (s(0) through s(5)) are collected as an array of
    these QVectors ( typedef QVector<OrbitData> OBArray[6] ).
  + The OBArrays for the Longitude, Latitude, and Distance are collected