d/rules: fix quotes in echo command

debian/rules

@@ -11,13 +11,13 @@ include /etc/os-release
 # the flag --supported-esm. Those versions are 0.18 and 0.14build1,
 # respectively. So we set specific distro-info requirements for bionic and later
 # versus Xenial to make those contraints applicable on each series.
-DISTRO_INFO_DEPS="distro-info (>= 0.18ubuntu0.18.04.1),"
+DISTRO_INFO_DEPS=distro-info (>= 0.18ubuntu0.18.04.1),
 
 ifeq (${VERSION_ID},"16.04")
-APT_PKG_DEPS="apt (>= 1.2.32), apt-transport-https (>= 1.2.32), apt-utils (>= 1.2.32), libapt-inst2.0 (>= 1.2.32), libapt-pkg5.0 (>= 1.2.32),"
-DISTRO_INFO_DEPS="distro-info (>= 0.14ubuntu0.2),"
+APT_PKG_DEPS=apt (>= 1.2.32), apt-transport-https (>= 1.2.32), apt-utils (>= 1.2.32), libapt-inst2.0 (>= 1.2.32), libapt-pkg5.0 (>= 1.2.32),
+DISTRO_INFO_DEPS=distro-info (>= 0.14ubuntu0.2),
 else ifeq (${VERSION_ID},"18.04")
-APT_PKG_DEPS="apt (>= 1.6.11), apt-utils (>= 1.6.11), libapt-inst2.0 (>= 1.6.11), libapt-pkg5.0 (>= 1.6.11),"
+APT_PKG_DEPS=apt (>= 1.6.11), apt-utils (>= 1.6.11), libapt-inst2.0 (>= 1.6.11), libapt-pkg5.0 (>= 1.6.11),
 endif
 
 %:
@@ -39,7 +39,7 @@ endif
 endif
 
 override_dh_gencontrol:
-	echo extra:Depends=$(APT_PKG_DEPS) $(DISTRO_INFO_DEPS) >> debian/ubuntu-pro-client.substvars
+	echo "extra:Depends=$(APT_PKG_DEPS) $(DISTRO_INFO_DEPS)" >> debian/ubuntu-pro-client.substvars
 	dh_gencontrol
 
 override_dh_systemd_enable: