golang: v↑ (1.9.4, 1.8.7)

Update go19 and go18 to their latest upstream versions bringing up bug and
security fixes.

Go19 tested briefly on neotest run.

/reviewed-by TrustMe

component/golang/buildout.cfg

@@ -34,8 +34,8 @@ make-targets= cd src && ./make.bash && cp -alf .. ${:location}
 
 [golang18]
 <= golang-common
-url = https://storage.googleapis.com/golang/go1.8.3.src.tar.gz
-md5sum = 64e9380e07bba907e26a00cf5fcbe77e
+url = https://dl.google.com/go/go1.8.7.src.tar.gz
+md5sum = c61cfe9c85e7d42f903d3fe146d7cde6
 
 # go1.8 needs go1.4 to bootstrap
 environment-extra =
@@ -43,8 +43,8 @@ environment-extra =
 
 [golang19]
 <= golang-common
-url = https://storage.googleapis.com/golang/go1.9.2.src.tar.gz
-md5sum = 44105c865a1a810464df79233a05a568
+url = https://dl.google.com/go/go1.9.4.src.tar.gz
+md5sum = 6816441fd6680c63865cdd5cb8bc1960
 
 # go1.9 needs go1.4 to bootstrap
 environment-extra =