Reduce captions' length of the screenshots in metainfo

Flathub's org.endlessos.Key with endless-key-flatpak v0.4 builds failed,
because the caption in metainfo is too long:

flatpak run --env=G_DEBUG=fatal-criticals --command=appstream-util org.flatpak.Builder validate builddir/*/share/appdata/org.endlessos.Key.appdata.xml
 in dir /srv/buildbot/worker/build-aarch64-5/build (timeout 1200 secs)
 watching logfiles {}
 argv: b'flatpak run --env=G_DEBUG=fatal-criticals --command=appstream-util org.flatpak.Builder validate builddir/*/share/appdata/org.endlessos.Key.appdata.xml'
 using PTY: False
builddir/files/share/appdata/org.endlessos.Key.appdata.xml: FAILED:
• style-invalid         : <caption> is too long [3. Resources such as finance, healthy body, TED Ed, sports, games, arts & crafts, gardening, and more];longest allowed is 100 chars
Validation of files failed

So, reduce captions' length by dropping the dot after the number.

Fixes: #66

data/metainfo/org.endlessos.Key.metainfo.xml.in.in

@@ -38,27 +38,27 @@
   <launchable type="desktop-id">@[email protected]</launchable>
   <screenshots>
     <screenshot type="default">
-      <caption>1. Bring equity into the classroom; curated learning anywhere, anytime with Endless Key</caption>
+      <caption>1 Bring equity into the classroom; curated learning anywhere, anytime with Endless Key</caption>
       <image type="source" width="1800" height="1013">https://raw.githubusercontent.com/endlessm/endless-key-flatpak/main/data/screenshots/1-equity.png</image>
     </screenshot>
     <screenshot>
-      <caption>2. Works online and offline; access learning resources for coding, STEM, cooking, and arts &amp; crafts!</caption>
+      <caption>2 Works online and offline; access learning resources for coding, STEM, cooking, and arts &amp; crafts!</caption>
       <image type="source" width="1800" height="1013">https://raw.githubusercontent.com/endlessm/endless-key-flatpak/main/data/screenshots/2-offline.png</image>
     </screenshot>
     <screenshot>
-      <caption>3. Resources such as finance, healthy body, TED Ed, sports, games, arts &amp; crafts, gardening, and more</caption>
+      <caption>3 Resources such as finance, healthy body, TED Ed, sports, games, arts &amp; crafts, gardening, and more</caption>
       <image type="source" width="1800" height="1013">https://raw.githubusercontent.com/endlessm/endless-key-flatpak/main/data/screenshots/3-tiles.png</image>
     </screenshot>
     <screenshot>
-      <caption>4. Engaging and interactive; discover an abundance of ready-made resources, games, simulations, etc</caption>
+      <caption>4 Engaging and interactive; discover an abundance of ready-made resources, games, simulations, etc</caption>
       <image type="source" width="1800" height="1013">https://raw.githubusercontent.com/endlessm/endless-key-flatpak/main/data/screenshots/4-interactive.png</image>
     </screenshot>
     <screenshot>
-      <caption>5. Completely free; access without an account, safeguarded data, and no ads</caption>
+      <caption>5 Completely free; access without an account, safeguarded data, and no ads</caption>
       <image type="source" width="1800" height="1013">https://raw.githubusercontent.com/endlessm/endless-key-flatpak/main/data/screenshots/5-free.png</image>
     </screenshot>
     <screenshot>
-      <caption>6. Grades 5–9, 2700+ curated resources, 1500+ videos, 300+ e-books</caption>
+      <caption>6 Grades 5–9, 2700+ curated resources, 1500+ videos, 300+ e-books</caption>
       <image type="source" width="1800" height="1013">https://raw.githubusercontent.com/endlessm/endless-key-flatpak/main/data/screenshots/6-list.png</image>
     </screenshot>
   </screenshots>