Update installer script to update subprojects first (#557)

Author: awvwgk

install.sh

@@ -42,7 +42,7 @@ done
 
 set -u # error on use of undefined variable
 
-SOURCE_URL="https://github.com/fortran-lang/fpm/releases/download/v0.3.0/fpm-0.3.0.F90"
+SOURCE_URL="https://github.com/fortran-lang/fpm/releases/download/v0.4.0/fpm-0.4.0.F90"
 BOOTSTRAP_DIR="build/bootstrap"
 if [ -z ${FC+x} ]; then
     FC="gfortran"
@@ -66,5 +66,6 @@ $FETCH $SOURCE_URL > $BOOTSTRAP_DIR/fpm.F90
 
 $FC $FFLAGS -J $BOOTSTRAP_DIR $BOOTSTRAP_DIR/fpm.F90 -o $BOOTSTRAP_DIR/fpm
 
+$BOOTSTRAP_DIR/fpm update
 $BOOTSTRAP_DIR/fpm install --compiler "$FC" --flag "$FFLAGS" --prefix "$PREFIX"
 rm -r $BOOTSTRAP_DIR