[cantarell-fonts/respacing] Add ShowInterpolation custom parameter

[Nikolaus Waxweiler <nwaxweiler src gnome org>]

commit 71e6e92d127b96ad030425f81c2ddae90afcace1
Author: Nikolaus Waxweiler <madigens gmail com>
Date:   Fri Jun 21 22:59:24 2019 +0100

    Add ShowInterpolation custom parameter

 src/Cantarell.designspace | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
---
diff --git a/src/Cantarell.designspace b/src/Cantarell.designspace
index 8ac6cb18..b01d3d6a 100644
--- a/src/Cantarell.designspace
+++ b/src/Cantarell.designspace
@@ -41,6 +41,17 @@
       <location>
         <dimension name="Weight" xvalue="80"/>
       </location>
+      <lib>
+        <dict>
+          <key>com.schriftgestaltung.customParameters</key>
+          <array>
+            <array>
+              <string>ShowInterpolation</string>
+              <string>-</string>
+            </array>
+          </array>
+        </dict>
+      </lib>
     </instance>
     <instance stylename="Regular Interpolated For Testing">
       <location>
@@ -56,6 +67,10 @@
                 <string>Regular</string>
               </array>
             </array>
+            <array>
+              <string>ShowInterpolation</string>
+              <string>-</string>
+            </array>
           </array>
           <key>com.schriftgestaltung.export</key>
           <false/>