Oops, don't make examples depend on a nonexistent feature.

It's a Cargo bug that this is not an error (and thus went unnoticed).

.test_like_travis.rb

@@ -9,7 +9,7 @@ travis_config['matrix']['include'].each do |env|
     ENV[$1] = $2
   end
   travis_config['script'].each do |cmd|
-    $stderr.puts('+ #{cmd}'.gsub(/\$(\w+)/) { ENV[$1] })
+    $stderr.puts('+ ' + cmd.gsub(/\$(\w+)/) { ENV[$1] })
     system(cmd)
   end
 end

Cargo.toml

@@ -52,19 +52,19 @@ required-features = ["std", "phy-raw_socket"]
 
 [[example]]
 name = "httpclient"
-required-features = ["std", "phy-tap_interface", "proto-ipv4", "socket-tcp"]
+required-features = ["std", "phy-tap_interface", "socket-tcp"]
 
 [[example]]
 name = "ping"
-required-features = ["std", "phy-tap_interface", "proto-ipv4", "socket-icmp"]
+required-features = ["std", "phy-tap_interface", "socket-icmp"]
 
 [[example]]
 name = "server"
-required-features = ["std", "phy-tap_interface", "proto-ipv4", "socket-tcp", "socket-udp"]
+required-features = ["std", "phy-tap_interface", "socket-tcp", "socket-udp"]
 
 [[example]]
 name = "client"
-required-features = ["std", "phy-tap_interface", "proto-ipv4", "socket-tcp", "socket-udp"]
+required-features = ["std", "phy-tap_interface", "socket-tcp", "socket-udp"]
 
 [[example]]
 name = "loopback"