[docs][ci] bump versions of R-package dependencies at RTD (#4488)

* remove R docs

* bump deps

docs/conf.py

@@ -256,13 +256,13 @@ def generate_r_docs(app):
         -y \
         -c conda-forge \
         -n r_env \
-            cmake=3.18.2=ha30ef3c_0 \
-            r-base=4.0.3=ha43b4e8_3 \
-            r-data.table=1.13.2=r40h0eb13af_0 \
-            r-jsonlite=1.7.1=r40hcdcec82_0 \
-            r-matrix=1.2_18=r40h7fa42b6_3 \
-            r-pkgdown=1.6.1=r40h6115d3f_0 \
-            r-roxygen2=7.1.1=r40h0357c0b_0
+            cmake=3.21.0=h8897547_0 \
+            r-base=4.1.0=hb67fd72_2 \
+            r-data.table=1.14.0=r41hcfec24a_0 \
+            r-jsonlite=1.7.2=r41hcfec24a_0 \
+            r-matrix=1.3_4=r41he454529_0 \
+            r-pkgdown=1.6.1=r41hc72bb7e_0 \
+            r-roxygen2=7.1.1=r41h03ef668_0
     source /home/docs/.conda/bin/activate r_env
     export TAR=/bin/tar
     cd {CURR_PATH.parent}