fix/snap: specify platforms to build for and drop i386 (#251)

Signed-off-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

snap/snapcraft.yaml

@@ -7,6 +7,23 @@ description: Python command-line client for tldr pages.
 grade: stable
 confinement: strict
 
+platforms:
+  amd64:
+    build-on: [amd64]
+    build-for: [amd64]
+  arm64:
+    build-on: [arm64]
+    build-for: [arm64]
+  armhf:
+    build-on: [armhf]
+    build-for: [armhf]
+  ppc64el:
+    build-on: [ppc64el]
+    build-for: [ppc64el]
+  s390x:
+    build-on: [s390x]
+    build-for: [s390x]
+
 parts:
   tldr:
     plugin: python