[librsvg: 17/19] Bump rustc requirement to 1.40

[Federico Mena Quintero <federico src gnome org>]

commit 12921c5c6d3e9504c95163baeaab4b731f53377c
Author: Federico Mena Quintero <federico gnome org>
Date:   Fri Aug 21 12:49:20 2020 -0500

    Bump rustc requirement to 1.40
    
    This for Option::as_deref()

 COMPILING.md | 2 +-
 configure.ac | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/COMPILING.md b/COMPILING.md
index b37f7d4ab..6e3e80ab1 100644
--- a/COMPILING.md
+++ b/COMPILING.md
@@ -32,7 +32,7 @@ minimum version is listed here; you may use a newer version instead.
 **Compilers:**
 
 * a C compiler and `make` tool; we recommend GNU `make`.
-* rust 1.39 or later
+* rust 1.40 or later
 * cargo
 
 **Mandatory dependencies:**
diff --git a/configure.ac b/configure.ac
index 986fadc58..1c6f5f43c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -114,7 +114,7 @@ AS_IF(test x$RUSTC = xno,
 dnl Minimum version of rustc that we support
 dnl If you change this, please update COMPILING.md
 MINIMUM_RUST_MAJOR=1
-MINIMUM_RUST_MINOR=39
+MINIMUM_RUST_MINOR=40
 
 rust_version=`$RUSTC --version`
 version=`echo "$rust_version" | sed -e 's/^rustc //g'`