v1.6.3.73 style: frun_GR6J subroutine is compliant with Fortran 95 standard

Reviewed-by: @antoine.pelletier
Refs #68

DESCRIPTION

 Package: airGR
 Type: Package
 Title: Suite of GR Hydrological Models for Precipitation-Runoff Modelling
-Version: 1.6.3.72
-Date: 2020-11-23
+Version: 1.6.3.73
+Date: 2020-11-24
 Authors@R: c(
   person("Laurent", "Coron", role = c("aut", "trl"), comment = c(ORCID = "0000-0002-1503-6204")),
   person("Olivier", "Delaigue", role = c("aut", "cre"), comment = c(ORCID = "0000-0002-7668-8468"), email = "airGR@inrae.fr"),

NEWS.md

@@ -4,7 +4,7 @@
 
 
 
-### 1.6.3.72 Release Notes (2020-11-23)
+### 1.6.3.73 Release Notes (2020-11-24)
 
 #### New features
 

src/frun_GR6J.f90

@@ -296,19 +296,14 @@
       IF(AR.GT.33.)  AR=33.
       IF(AR.LT.-33.) AR=-33.
 
-      IF(AR.GT.7.)THEN
+      IF(AR.GT.7.) THEN
         QRExp=St(3)+Param(6)/EXP(AR)
-      GOTO 3
-      ENDIF
-
-      IF(AR.LT.-7.)THEN
+      ELSEIF(AR.LT.-7.) THEN
         QRExp=Param(6)*EXP(AR)
-      GOTO 3
+      ELSE
+        QRExp=Param(6)*LOG(EXP(AR)+1.)
       ENDIF
 
-      QRExp=Param(6)*LOG(EXP(AR)+1.)
-    3 CONTINUE
-
       St(3)=St(3)-QRExp
 
 ! Runoff from direct branch QD