Use fxtag to specify RRTMGP external tags.

.gitmodules

@@ -35,8 +35,8 @@
 
 [submodule "cdeps"]
     path = components/cdeps
-    url = https://github.com/jedwards4b/CDEPS.git 
-    fxurl = https://github.com/ESCOMP/CDEPS.git 
+    url = https://github.com/jedwards4b/CDEPS.git
+    fxurl = https://github.com/ESCOMP/CDEPS.git
     fxtag = cdeps1.0.24_rme1
     fxrequired = T:T
 
@@ -110,7 +110,7 @@
     fxtag = pio2_6_2
     fxrequired = T:T
 
-[submodule "mct"] 
+[submodule "mct"]
     path = libraries/mct
     url = https://github.com/MCSclimate/MCT
     fxurl = https://github.com/MCSclimate/MCT
@@ -183,8 +183,8 @@
 [submodule "rte-rrtmgp"]
 	path = src/physics/rrtmgp/ext
 	url = https://github.com/earth-system-radiation/rte-rrtmgp.git
-	branch = v1.7
+        fxtag = v1.7
 [submodule "rrtmgp-data"]
 	path = src/physics/rrtmgp/data
 	url = https://github.com/earth-system-radiation/rrtmgp-data.git
-	branch = v1.8
+        fxtag = v1.8