gitian: don't add . to tar list

Since permissions and timestamps are changed for the sake of determinism,
. must not be added to the archive. Otherwise, tar may try to modify pwd when
extracting.

contrib/gitian-descriptors/gitian-linux.yml

@@ -99,7 +99,7 @@ script: |
     find . -name "lib*.la" -delete
     find . -name "lib*.a" -delete
     rm -rf ${DISTNAME}/lib/pkgconfig
-    find . | sort | tar --no-recursion --mode='u+rw,go+r-w,a+X' --owner=0 --group=0 -c -T - | gzip -9n > ${OUTDIR}/${DISTNAME}-${i}.tar.gz
+    find ${DISTNAME} | sort | tar --no-recursion --mode='u+rw,go+r-w,a+X' --owner=0 --group=0 -c -T - | gzip -9n > ${OUTDIR}/${DISTNAME}-${i}.tar.gz
     cd ../../
   done
   mkdir -p $OUTDIR/src

contrib/gitian-descriptors/gitian-osx.yml

@@ -126,7 +126,7 @@ script: |
     find . -name "lib*.la" -delete
     find . -name "lib*.a" -delete
     rm -rf ${DISTNAME}/lib/pkgconfig
-    find . | sort | tar --no-recursion --mode='u+rw,go+r-w,a+X' --owner=0 --group=0 -c -T - | gzip -9n > ${OUTDIR}/${DISTNAME}-${i}.tar.gz
+    find ${DISTNAME} | sort | tar --no-recursion --mode='u+rw,go+r-w,a+X' --owner=0 --group=0 -c -T - | gzip -9n > ${OUTDIR}/${DISTNAME}-${i}.tar.gz
     cd ../../
   done
   mkdir -p $OUTDIR/src

contrib/gitian-descriptors/gitian-win.yml

@@ -106,7 +106,7 @@ script: |
     find . -name "lib*.la" -delete
     find . -name "lib*.a" -delete
     rm -rf ${DISTNAME}/lib/pkgconfig
-    find . -type f | sort | zip -X@ ${OUTDIR}/${DISTNAME}-${i}.zip
+    find ${DISTNAME} -type f | sort | zip -X@ ${OUTDIR}/${DISTNAME}-${i}.zip
     cd ../..
   done
   mkdir -p $OUTDIR/src