gnupg2: fix shell path

packages/gnupg2/build.sh

@@ -1,6 +1,7 @@
 TERMUX_PKG_HOMEPAGE=https://www.gnupg.org/
 TERMUX_PKG_DESCRIPTION="Implementation of the OpenPGP standard for encrypting and signing data and communication"
 TERMUX_PKG_VERSION=2.2.8
+TERMUX_PKG_REVISION=1
 TERMUX_PKG_SHA256=777b4cb8ced21965a5053d4fa20fe11484f0a478f3d011cef508a1a49db50dcd
 TERMUX_PKG_SRCURL=https://www.gnupg.org/ftp/gcrypt/gnupg/gnupg-${TERMUX_PKG_VERSION}.tar.bz2
 TERMUX_PKG_DEPENDS="libassuan,libbz2,libgcrypt,libksba,libsqlite,libnpth,readline,pinentry,libgpg-error"

packages/gnupg2/g10-exec.c.patch

@@ -0,0 +1,12 @@
+diff -uNr gnupg-2.2.8/g10/exec.c gnupg-2.2.8.mod/g10/exec.c
+--- gnupg-2.2.8/g10/exec.c	2017-08-28 13:22:54.000000000 +0300
++++ gnupg-2.2.8.mod/g10/exec.c	2018-06-19 19:08:38.918070875 +0300
+@@ -383,7 +383,7 @@
+ 	  char *shell=getenv("SHELL");
+ 
+ 	  if(shell==NULL)
+-	    shell="/bin/sh";
++	    shell="@TERMUX_PREFIX@/bin/sh";
+ 
+ 	  /* I'm the child */
+