Updated CTA text

ref DES-164

ghost/email-service/lib/email-templates/partials/paywall.hbs

@@ -3,9 +3,9 @@
         style="position: relative; display: block; width: 100%; margin: 3em 0; padding: 0; height: 1px; border: 0; border-top: 1px solid #e5eff5;">
     <h2
         style="margin-top: 0; font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; line-height: 1.11em; font-weight: 700; text-rendering: optimizeLegibility; margin: 1.5em 0 0.5em 0; font-size: 26px;">
-        Subscribe to <span style="white-space: nowrap; font-size: 26px !important;">continue reading.</span></h2>
+        Upgrade to <span style="white-space: nowrap; font-size: 26px !important;">continue reading.</span></h2>
     <p style="margin: 0 auto 1.5em auto; line-height: 1.6em; max-width: 440px;">Become a paid member of {{site.title}} to get access to all
-    <span style="white-space: nowrap;">subscriber-only content.</span></p>
+    <span style="white-space: nowrap;">premium content.</span></p>
     <div class="btn btn-accent" style="box-sizing: border-box; width: 100%; display: table;">
         <table border="0" cellspacing="0" cellpadding="0" align="center"
             style="border-collapse: separate; mso-table-lspace: 0pt; mso-table-rspace: 0pt; width: auto;">
@@ -16,7 +16,7 @@
                         valign="top" bgcolor="{{accentColor}}">
                         <a href="{{paywall.signupUrl}}"
                             style="overflow-wrap: anywhere; border: solid 1px #3498db; border-radius: 5px; box-sizing: border-box; cursor: pointer; display: inline-block; font-size: 14px; font-weight: bold; margin: 0; padding: 12px 25px; text-decoration: none; background-color: {{accentColor}}; border-color: {{accentColor}}; color: #FFFFFF;"
-                            target="_blank">Subscribe
+                            target="_blank">Upgrade
                         </a>
                     </td>
                 </tr>