Fix typo in macro expanding syntax

bisq-exchange.spec.in

@@ -32,7 +32,7 @@ The decentralized bitcoin exchange https://bisq.network
     mkdir -p "%{buildroot}/opt/bisq-exchange" "%{buildroot}%{_bindir}"
     cp -r ./[a-z0-9]* "%{buildroot}/opt/bisq-exchange"
     install -m 0755 bisq-exchange "%{buildroot}/opt/bisq-exchange"
-    ln -sT "/opt/bisq-exchange/bisq-exchange" "%{buildroot}${_bindir}/bisq-exchange"
+    ln -sT "/opt/bisq-exchange/bisq-exchange" "%{buildroot}%{_bindir}/bisq-exchange"
     find "%{buildroot}/opt/bisq-exchange" | LC_ALL=C sort > all.list
     find "%{buildroot}/opt/bisq-exchange" -type d | LC_ALL=C sort > dirs.list
     sed -i -e "s|^%{buildroot}||" all.list dirs.list