Use the canonical abbreviation "pc" of pica, instead of "pi"

like as fixed at 8a5b178e.
This change affects e.g. the string of the tooltip appearing
when changing document margin in Writer by dragging ruler,
after choosing pica as the unit in context menu.

Change-Id: I55d2cea8b30016e2578c6a112f54e26d62741b44
Reviewed-on: https://gerrit.libreoffice.org/43819Reviewed-by: Julien Nabet <serval2412@yahoo.fr>
Tested-by: Takeshi Abe <tabe@fixedpoint.jp>

svtools/source/control/ruler.cxx

@@ -118,7 +118,7 @@ static const RulerUnitData aImplRulerUnitTab[RULER_UNIT_COUNT] =
 { MapUnit::Map100thInch,     1200,   120.0,   120.0,    600.0,   1200.0,  "'"      }, // FOOT
 { MapUnit::Map10thInch,    633600, 63360.0, 63360.0, 316800.0, 633600.0,  " miles" }, // MILE
 { MapUnit::MapPoint,             1,    12.0,    12.0,     12.0,     36.0,  " pt"    }, // POINT
-{ MapUnit::Map100thMM,        423,   423.0,   423.0,    423.0,    846.0,  " pi"    }, // PICA
+{ MapUnit::Map100thMM,        423,   423.0,   423.0,    423.0,    846.0,  " pc"    }, // PICA
 { MapUnit::Map100thMM,        371,   371.0,   371.0,    371.0,    743.0,  " ch"    }, // CHAR
 { MapUnit::Map100thMM,        551,   551.0,   551.0,    551.0,   1102.0,  " li"    }  // LINE
 };